For some of these old timers that are getting banned I wonder if these people have bought these accounts that were farmed via spamming/copy and pasting? I doubt someone would forget that they've done this in the past, or maybe they're just playing dumb. It's very surprising how many users have done it and even more so for how long they got away with it.
If this is true and those currently using the accounts are going to be held to account for the plagiarism of the farmer, we might as well ban account sales, even if you cant prevent all of them. I dont think it is reasonable to expect someone to check for plagiarism when they buy an account, or even know how to effectively check. This way if someone is banned for plagiarism the farmer did, there wouldnt be an injustice because they should have been banned for using the purchased account anyway (or the purchased account should have been locked).
I dont think it would be difficult to generally tell if a person in good standing had purchased their account after the time of plagiarism.