Question regarding adopting a new pet

So I've spent the better half of this last week reading and researching in preparation to adopt a new kitten. I do have an existing cat and that normally wouldn't be a problem. I read here that I would need to obtain a license for them which I've never heard of before. It states, "A valid veterinarian certificate showing the rabies tag number and the expiration date is required. When applicable, please also include documentation showing that the animal is spayed or neutered." I can probably get this information for the new kitten, but for my existing cat, this could get problematic. She has all her shots and is neutered but I no longer have information on anything that states that this happened. No records, nothing. Why? because this happened way back in 2007 when my cat was around 3 months old, and I was a minor at the time and everything was handled by my mom. I asked her about it and I shit you not she says with a straight face, "oh yeah I lost that when we moved. I didn't think it would be that important."

W H A T.

I can't reach out to the clinic that originally did this because that clinic was in another state, and was shuttered in 2018. Plus I'm not sure they could pull up something from 15 years ago. I don't want to lie and say I don't have another cat cause if something comes up and they find out about it, I'll be screwed. I know this probably isn't something I should be really concerned about but this is my first time doing this on my own, and as someone who doesn't have the cleanest history with the law (I've never been arrested or charged, but I've been on CPD's radar for some time, none of which were animal abuse or domestic violence-related) I don't want to take any risks.

Any and all help is appreciated. Thank you.