Actually, 18 USC § 1621 > (2) in any declaration, certificate, verification, or statement under penalty of perjury as permitted under section 1746 of title 28,

Actually, 18 USC § 1621 > (2) in any declaration, certificate, verification, or statement under penalty of perjury as permitted under section 1746 of title 28, United States Code, willfully subscribes as true any material matter which he does not believe to be true; If you don't remember the handles, they have to prove that you didn't believe that you made a true declaration. Maybe putting a note of "Various other accounts on various platforms I cannot recall the usernames of" would address that? Not a lawyer. That statute conveniently lets you forget things, just not blatantly lie. Had a twitter account a year ago that you forgot about? You could forget about it. Tweeted on it yesterday? Not so much. It's an impossible case to prove, as the bar for perjury if not under oath is much higher. They have to prove that you didn't believe the stated information to be true.