I used Windows 2.01 at the time, and I deployed NT 3.1 in production.
Your claim is wrong. You said that the first Windows not based on DOS was 2000; that is not true. The first Windows not based on DOS was in 1993.
What name Microsoft marketing put on it is irrelevant. If you opened a command prompt on Windows 2000 and typed `ver`, it said Windows NT 5.0.
Do not get misled by branding. As Terry Pratchett said:
"Zoon tribes are very proud of their Liars. Other races get very annoyed about all this. They feel like the Zoon ought to have adopted more suitable titles, like ‘diplomat’ or ‘public relations officer.’ They feel they are poking fun of the whole thing."
- Equal Rites
Marketing means lying. Marketing took the letters "NT" out of Windows 2000's name, but that does not mean it was the first product of its kind. It was not. It was the fifth.