VISA apps are submitted online/electronically, and as far as I know may have been “auto-approved” by a computer w/o human intervention (before 2001)(they are interviewed by embassy/consular staff in advance of issuing a VISA nowadays).
Lots of errors on the VISA apps and they got approved anyway (Leftie leaning site, but lots of relevant info.):
https://longislandwins.com/resources/immigration-101/how-the-911-highjackers-got-into-the-us/
Other info.:
https://abcnews.go.com/WNT/story?id=130051&page=1
https://govinfo.library.unt.edu/911/staff_statements/staff_statement_1.pdf
“as far as I know”
“leftie leaning site” ...
Come on these are not authoritative sources. Mine are just as believable and contradict
Let people decide what they want