I'd suggest that the sort of JW who says 1975 never happened may be the sort of JW it's not worth arguing with. It's not like decades ago when ignorance on this topic, as many other topics, may have been excusable. Anyone who wants to find out what happened around 1975 can do so easily in a few clicks. If they insist nothing happened around 1975 they are either wilfully ignorant or lying. And you can't force anyone to learn or accept something they don't want to.
I have a JW who from time to time tries to convince me evolution is false. I guess I've kind of humoured it over the years. He points to new magazines on design or whatever. But what I should really say to him, because he's obviously never read a book on evolution, is simply that he should read an actual book on he subject then we could have a meaningful conversation. For perhaps 99% of people who say they don't accept evolution, the only information that comment conveys about the person is that they've never actually read a book that explains the subject rather than distorts it. They have nothing meaningful to say about the subject itself because they don't really know anything about it.
Same thing when a JW says "I've never heard that 1975 was a thing". They somehow think this means "because I don't know about 1975 being a thing, therefore 1975 wasn't a thing". This is obviously specious logic. It's just as bad as saying "I find evolution incredible therefore it can't be true". These sorts of statements say nothing about the topic in itself and everything about the wilful ignorance of the person making the statement.