The sites that you said addressed the myth might be working with spamming companies or be the spammers themselves. I don't know that much about spam, but it appears to not be the same as telling someone to take you off their mailing list when they call you.
Several other sites agree with the fact that you should not unsubscribe from spammers as it does the following-
The typical advice from anti-spam groups is to not even try to use
their "unsubscribe" methods, since that confirms for the spammer that
the address is not only good (thus: send it more spam!) but also that
the recipient actually opens spams sent there (thus: send it even more
Also, from this we can see that people have done other test for this.
This qoute outlines that clicking unsuscribe is the wrong course of action.
Before you answer, in most cases the spammers are just guessing at
email addresses. Fill out the ‘unsubscribe” line, and the guesswork is
over: they know they have a live one. Worse, said Maiffret: "In
reality, that's usually an indicator to increase the level of things
they send to you. We even see when you click unsubscribe, it'll take
you to a website and the website will actually try and attack against
your computer," he explained
Filipiak had to change his email address, as this reporter will also
have to do. For this article, I clicked "unsubscribe" on two weeks’
worth of spams; more than 125 times. My daily spam average is on the
rise, with no signs of slowing down. With spam accounting for an
estimated 80 percent of all email traffic in the United States, the
spammers don’t appear to be slowing down, either. The best option,
experts said, is to choose the "Mark as Junk" option provided by some
email providers. If that’s not an option, just hit "delete" and move
As for "Do spammers actually compile lists of "known deliverable email addresses"?" I couldn't find any info to support that, but from the volume of mail these people were sent other spammers were probably in on it.
I did however find numerous accounts of people's e-mails sending other people spam, which if they unsubscribe can give the spammers more accounts. I found this by googling "unsuscribing to spam gets you more spam"(the results were to many).