Intelligence agencies around the world are believed to be combing through the files, which are believed to be genuine, for vital information on foreign fighters and their networks at home.
The 23-part surveys detail extremists’ names, birth dates, nationalities, hometowns, nationalities and even blood types.
There is also a slot for members to choose if they want to be used as suicide bombers, soldiers or in another role, and to name a referee who “recommended” them to the group.
In the documents, Amimour, Mohamed-Aggad and Mostefai – all from France - said they wanted to fight for Isis when they arrived, though it was possible to tick an option on the form to be a suicide attacker, German media reported.
The cache showed that at least 14 men from France crossed the Turkish-Syrian border with their families on 18 December 2013 with the same smuggler and were vouched for by a single extremist of Moroccan origin, it said. Mohamed-Aggad was one member of that group.
He was reportedly shot by police as they stormed the Bataclan, while Amimour and Mostefai blew themselves up.
Abdelhamid Abaaoud, the Belgian suspected ringleader of the Paris attacks, also appears in the documents under his war name Abu Omar al-Beljiki as a guarantor for other French Islamists, the Süddeutsche Zeitung reported.
Shiraz Maher, a senior research fellow at the International Centre for the Study of Radicalisation at Kings College in London, said that the information was “key” to tracing international terrorist networks and facilitators.
“By cross-checking these names against the information we have already, we'll be likely to piece together a detailed picture of Isis networks and how they relate to one another,” he added.
Süddeutsche Zeitung is one of three German outlets with access to the 22,000 files, alongside broadcasters WDR and NDR.
Sky News was also handed the registration forms, reportedly on a memory stick stolen from the head of the Islamic State group's internal security police by a disillusioned fighter.
They were first published by Zaman al-Wasl, a Syrian pro-opposition website that said they revealed the names of 1,736 fighters from around 40 countries. Many are believed to be duplicated on the 22,000 forms from 2013 and 2014.
The editor, Mohamed Hamdan, said the database was handed over in December by a Syrian man who is now in Turkey but the site held off publishing immediately.
"There are those who want a scoop,” he added. “But for us, we have a moral objective, because if we publish the names, there are consequences for their loved ones.”
Zaman al-Wasl refuses to cooperate with intelligence services but Germany's federal criminal police has confirmed it possesses the files, which will be shared through Europol.
Robert Wainwright, director of the European police organisation, said: “If the provenance and accuracy of the information is confirmed it undoubtedly represents a significant intelligence gain for Western authorities and should be exploited fully.”
Some analysts have cast doubt on the authenticity of the files, highlighting inconsistencies, but counter-terrorism officials are said to be treating them as legitimate and the details of previously known Isis militants, such as British members Abdel Bary, Junaid Hussain and Reyaad Khan, are said to match up.
Afzal Ashraf, a visiting fellow at Nottingham University’s centre of conflict, security and terrorism, told The Independent the leak will be “devastating” for the terrorist group.
“It will be a great blow for their recruitment process because these documents show not just the people joining but the networks involved in radicalising them and facilitating their travel,” he said.
“Any recruit will know they are very likely to be discovered and there will be serious consequences for them, it doesn’t inspire a great deal of confidence.”
Mr Ashraf added that claims a disillusioned Isis member leaked the files could spark damaging internal purges, executions and in-fighting.
As of last month, the US estimates Isis has 19,000 to 25,000 fighters in Iraq and Syria, down from a peak of up to 31,500.
Additional reporting by AP
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