So you deposit this money in an exchange: You already have problems explaining the origin of the funds. The funds may or not be accepted. Then if you ever got out of that situation, you would need to prove authorities source of funds to the last sat. The fact that they don't have KYC is already a problem, but since this was ages ago you did not keep 100% of records, some websites are missing, etc. You also advertised mixers, so it's questionable how they would react.
But if you want to go this way, depending on the country where you live, you can simply declare that you got paid for marketing etc., so you can just pay taxes on this income.
I don't really understand the pickle, unless you live in a country where everything related with bitcoin (holding, earning, buying) is illegal, in which case, I don't think we should be having this conversation at all.