The Rover Group, which is organising a Mini rally at Silverstone race track on 22-23 August, has been trying to trace a "full set" of the 133 models made at its Longbridge plant over the years.
An appeal in the IoS three weeks ago brought a flood of letters from readers, some of whom are planning to seize the opportunity to exhibit their cars in a Mini hall of fame at Silverstone.
Among the rare models owned by readers are a lime green 1981 Mini 1000 city saloon, a limited edition1988 Mini Flame, a yellow limited edition 1983 Mini Sprite, a 1988 limited edition Mini Jet Black and a red 1979 Mini 850 City.
Caroline Skinner, 17, of Ticknall, in Derbyshire, wrote to say that she was learning to drive on a 1988 blue and white limited edition Mini Sky.
Many of the letters make plain that the Minis are their owners' pride and joy. Some readers enclosed photographs of their cherished cars. Chris Matoza, from Liverpool, wrote: "I have a 1993 Mini Rio. She's black, she's beautiful and she's called Martha."
Matthew Taylor, of Exmouth, Devon, sent a picture of his 1990 Mini Checkmate (black with a white roof) which could, he said proudly, reach 90mph.
Ian House, of Deal, Kent, owns a 1989 Mini Rose, a striking model which is white with a pink roof. Giving a short biography of the car, he says that in late 1993 "the arrival of a German Shepherd puppy forced her sale to a local garage".
Eventually "she was sold to her current owner whilst on a visit to Deal, Kent, where she currently resides". Mr House writes that he would be honoured to exhibit her at Silverstone if she was deemed to be in good enough condition.
Rebecca Rickard, of south-west London, sent a Polaroid of her 1995 Mini Cooper 1.3i. She wrote: "Although it is not a rare model, it is in excellent condition and very pretty, with its alloy wheels and nudge bars."
Possibly the Mini's longest-standing admirer is 90-year-old Methar Kagan, of Solihull, West Midlands, who still drives and has one of the missing models: a 1982 automatic 1000HLE saloon.
Mrs Kagan comes from a family of Mini enthusiasts. Her son, Roger, and his wife, owned a Mini Broadspeed and a Minivan in the Sixties, and her grandson, Gavin, has a Mini Sprite.
A love of Minis does seem to run in the family. Tim Baker wrote from Caterham, Surrey, to say that he and his brother both owned black 1990 Mini Coopers and enclosed a photograph of them side by side.
Mini owners are also, it seems, inventive. Roger Kagan recalled in his letter that in 1968 an acquaintance who lived near Longbridge demonstrated to him a Minivan that he had devised to run on a mixture of lighter fuel, water and molybdenum.
As the Silverstone rally approaches, just 30 models are still missing. Rover said yesterday that it was extremely grateful for IoS readers' contributions to the birthday celebrations. "The Independent on Sunday has been a tremendous help in attempting to trace the full set," said Paula Joyce, a Rover spokeswoman.