What is the best public, unambiguous, non-YouTube reference I can cite for
the late David Mills' initial FTP work?

I see that the wording on his Wikipedia page has the ambiguous phrase "had
the first implementation of FTP", which has been flagged as needing
clarification, so I intend to provide it.

In both this interview:

https://conservancy.umn.edu/bitstream/handle/11299/113899/oh403dlm.pdf

... and this video recording of Mills himself giving a lecture at UDel:

https://youtu.be/08jBmCvxkv4?t=428

... it's quite clear that it's literally true - he authored, compiled,
installed, implemented, and tested the very first (and apparently second)
FTP server. But Wikipedia's guidelines discourage YouTube-only citations,
and the text in the interview seems insufficiently detailed to have
citation value.

What is the best reference I can cite?

Thanks!

-- 
Royce