I just came across this thread and wanted to show you mine.
I was there, and paid & watched Stan Lee sign this comic, and then paid more right after for this COA. Is the COA itself legit? Probably... but with out a tiny bit of doubt, Lee's signature on my comic is absolutely legit.
Mind you, it was signed in April of 2017 and he was 94 years old... *and still kickin arse* so it's not his usual clear & legible signature, but his none-the-less.
He died the following year, so I am grateful I got it. Hope this helps in determining your authenticity... I personally think yours are the real thing.