Do you disagree? In your opinion.
Whether I agree or disagree does not make your statement any more or less of a fact.
I actually do know of some people around that time who only had their answer phone on when they were out of the house, however I certainly wouldn’t pretend to know if these people were in the majority or minority, I personally didn’t have one then so couldn’t comment on what I’d have done at the time. It’s worth considering though that many answerphones cut in after a small number of rings - a bit like all calls now going to voicemail after a couple of rings rather than an extended time period to allow someone to answer, would voicemail be treated differently now if all calls went very quickly to it?
You consistently demand that any view that is in opposition to yours is backed up by sources for each statement and regularly post that any statement not backed up by sources has to be discounted, therefore you need to play by your own rules, Either prove that everyone had their answer phones on 24/7 or stop stating it as a fact.