It's not LITERALLY true that every single event and story in every regular title was reflected or acknowledged in the others, but when there was necessity to do so for the sake of the stories, then Yes, there was acknowledgement of what was happening in, say, Iron Man or Spider Man.
The good thing was that the editors at Marvel then didn't feel the need to harnass all the titles into long semi-cross-overs and 'tie-ins' as today, when the MU has become reductive and claustrophobic, with one mindless disaster after another---look how many times the X-mansion has been destroyed in the last 5 years--3? 4? 5? It's absurd.
Then, seemingly out of the blue, we could get a cool FF single issue featuring a new attack by Diablo, or the reemergence of the Brute, or, in Daredevil, a scheme by the Jester or the Death-Stalker, or the Hulk might come upon an alien colony in the Nevada desert.
There was a sense of freedom and that anything could happen--and everything did!
And when an acknowledgement of what was happening in another title was seen as necessary or desirable, we saw it.
It was a unified universe of great complexity.
Quite the opposite of what we have before us today for the most part. Only 'Conquest' and a few other mini-series have that feel.
And 'Conquest' does a hugely admirable job of it, with the Super Adaptoid, Ultron, Blastaar, Moondragon, Adam Warlock, Mantis, Groot, the Dragon of the Moon, Star Lord, Ronan, the Wraith, and others all beautifully presented--and accurately.
And yes, the characters in Conquest actually progress and move forward as characters! Heavens. The X-franchise should be so lucky, and the Avengers too.
It's almost too much to expect from Marvel today, which isn't marvelous by and large, with its tepid New Avengers, HOM, Civil War, M-Day crap, etc.
Conquest gives us the 'sense of wonder, which I think is all-important to this medium.