This is a milestone that, ironically, Stewart himself could well have been celebrating had the England captaincy, following Graham Gooch's resignation four and a half years ago, remained with the yeomanry, instead of falling into Oxbridge hands.
For Stewart, 35 at the end of the tour, such conjecture and speculation are as pointless as patting back a juicy half-volley and then moaning about the missed opportunity. Even so, as Atherton's long-term opening partner, he is perhaps well placed to have noticed how the half-century, unique to English cricket at least, has been constructed.
"Athers has improved tactically and he handles tough situations much better than he did when he first started. I'd say it's only his handling of individuals, which he does in his own way, which is still a bit unusual. It agrees with some players, but not with others, and it's more a case of them having to get used to him than the other way round."
But if their viewpoints do not always meet on common ground, Stewart is a loyal admirer, and one of those who phoned Atherton at the 11th hour to try and talk him out of resigning the captaincy - a ploy which eventually succeeded.
"I simply said: if you're quitting because you feel it's affecting your batting, fair enough. But if it was for the wrong reasons, like media pressure, then he should carry on as we probably had our best chance ever of beating the West Indies. I told him, after all he'd been through, he deserved to be captain of what could be a successful England side."
They have a chance, too, and one that, with the series level at one Test apiece, is so far being sustained by Stewart's bat and Angus Fraser's unstinting efforts with the ball.
With 259 runs in two Tests and a farce, all on fairly spiteful pitches, Stewart is way ahead of the chasing pack. Mind you, it is not the first time he has done well in the Caribbean and, since the Packer era began in 1977 - a time when the West Indies pace bowling juggernaut had just begun to roll into action - no visiting player has scored more runs.
"I'm generally a fluent timer of the ball, but I'd rate my 83 in the last innings of the second match in Trinidad, which took nearly five hours, as one of the best I've ever played. Batting against this lot is always a challenge but in those conditions I had to work much harder, and from a defensive and concentration point of view, it's as well as I've played."
A hard-working cricketer, he analyses his game closely, usually after consultation with his father, Mickey, who was England coach from 1986- 1992, and is a man who knows his son's game blindfold.
"With the pitches so far having a tendency to keep low as well as move about, I've deliberately stayed leg side of the ball," Stewart said. "Normally I go back and across to off stump, but if you do that and the ball squats, chances are you're going to play across it and be lbw. By staying fractionally out of line, and keeping my pads out of the way, I hope to get a bat on it instead.
"Mind you, Dad phoned me two days ago to remind me to go back to my old ways when I get on truer pitches, which with a bit of luck will happen in this Test, which is normally a good surface."
In fact, the pitch at the Bourda ground in Georgetown is fairly bare, and may suit spin. It is a suspicion even entertained by the West Indies selectors, who have picked a specialist wrist spinner, Dinanath Ramnarine - a selection that may persuade England to play both of their slow bowlers in the fourth Test.
As far as England are concerned, the problems over accommodating an extra spinner are well known. In the past, it has mainly been the wicket-keeper who has made way, with Stewart having to soak up the extra responsibility of taking the gloves. But while he is again willing to do whatever is asked of him, England appear to be intent on resolving the dilemma by other means.
"I enjoy keeping and I'll do it if asked. But you also have to ask what is best for the team and I think a major strength of this team is an Atherton/Stewart opening partnership. If I had to keep, I couldn't open as well and I can't see us going that route with three Tests still left to play."
As a batsman recently on the sharp end of Ambrose and Walsh, he scoffs at the recent notion that they are over the hill. "Whatever happened in Pakistan happened. As far as I'm concerned Amby [Ambrose] has bowled as well as I can remember. OK, the pitches and the large seams on the balls have undoubtedly been a factor, but he just doesn't bowl a bad ball.
"He makes it look so simple too. He just runs in straight, his arm comes over straight, he follows through straight and the ball goes straight. Which is what Gussie [Fraser] does for us, at a slightly reduced pace.
"During the two Tests in Trinidad, the only boundary I can remember scoring off Ambrose was a thick edge to third man. Courtney is similar, though he might give you a few more balls to score off. Against bowlers like that you have to limit your ambition. I'm reading Steve Waugh's diary of their tour here three years ago and he' right when he says you can't look further ahead than the next ball. You simply can't set scoring targets like you might against other teams."
As a touchstone, and simply as a reminder that it can be done, he carries a video of his back-to-back hundreds, made in Barbados four years ago, around with him.
"I'm a great believer in watching videos of yourself, and it's good to compare how I'm batting now with those knocks then, which I consider to be two of my best ever."
But if Barbados holds special cricketing memories, it is also the place where wives and significant others descend, and Stewart is looking forward to seeing his family, a visit that was banned last winter in Zimbabwe. "Last winter's decision to ban wives and girlfriends was wrong. As long as they realise that we are working and that they are only here because we're working, that's fine. I'm lucky, my wife Lynne knows where she stands when the cricket's on. But as long as they are well organised, which they weren't in Cape Town two winters ago, it shouldn't be a problem. After all, as we proved in Zimbabwe, we can lose without them being there as well."
With two young children growing up rapidly, many players find it increasingly difficult to drag themselves away on tour. It is a difficult situation, though one that Stewart - despite the absence of his own father, away touring with England during the 1960s - does not envisage changing just yet.
"While the family comes first, it's a career and one that has looked after me well. Providing fitness and form are not compromised, I want to play as long as possible. One of the greatest influences on my cricket has been Graham Gooch, who had his best years between the age of 34 and 39. As Linford Christie once said: `Age is just a number.' Well, I'm 35 in April and, as long as I keep enjoying it, I want to keep going."
A meticulous player before batting, he goes through the same habits of preparation: the twirling bat; the little scrape of the crease, as well as the little kick of dust as he wanders to square leg to compose himself. All have helped him add up to the formidable batsman he is today.
When I tell him that Ladbrokes have him to make 450-465 runs in the series, he feigns mock surprise, saying he'll be happy to settle for that. When I tell him it's a good deal higher than the spread offered on Brian Lara he laughs the laugh of a man at ease with himself. "It just shows you, they know nothing about the game," he said.
l The West Indian vice-captain, Carl Hooper, has been reported to the West Indies Cricket Board and could face disciplinary action for deciding not to play for Guyana against England last weekend. The West Indies coach, Malcolm Marshall, and the chairman of selectors, Les Hall, had instructed all their Test batsmen to play if possible between the third and fourth Tests, but Hooper ignored their advice.