How would someone convince the court that you never agreed to the TOS?

For example, I created my account before there was a TOS, and FB used easily-bypassable ways to get users to agree to a TOS, and eventually they stopped asking me, leading me to believe they think I agreed. Without my wet signature on anything, how can they prove I agreed to something when they can just flip a bit and claim their records show I did?

I guess the user would get a notice that FB/Meta filed something and that they could respond saying that's not true?