OP says "Anyone who went to grade school in the 1970s or 1980s probably saw something made by Bell and Howell..." This was certainly my experience (I'll add 1960s to the list of decades) and I believe it to be true generally (at least in North America.) We also saw a lot of SONY cassette tape recorders and video cameras back in the day. In both cases, this exposure very likely created lasting positive sentiment about the brands. That process was possibly subliminal. We tended to personally experience these products at special (and more interesting) times than normal classroom education. Also, again at least in my case, the products made by these brands just plain worked.
The point is that we experienced these brands as consumers. (Albeit possibly via the school system which would have had a more business to business relationship with these companies.) Without a doubt, the most experience that consumers would have had with IBM is the PC. But this experience was a lot less positive. Immediately upon creating this whole market, consumers discovered that IBM was by far the most expensive option. It has always been said of IBM "You can buy better but you can't pay more." The next discovery followed fairly quickly: third parties innovated much faster; you could get cooler new stuff faster by not buying IBM. By the time PCs had morphed into laptops, IBM had thrown in the towel. They admitted defeat in the PC operating system space and the sold the remnants of their PC business to Lenovo.
As a brand name, what are the letters IBM really worth down the road? The vast majority of the world have no particular interest in this name. IBM's customers are large businesses and some governments and those organizations tend not to have a lot of sentimental memory. They will use IBM products and services as long as they make more money than they cost. But they do not attach sentimental value to the name.
I never really understood those IBM ads for block chain (and other technical matters) on NFL broadcasts. Who is watching an NFL game and is suddenly struck by a desire to start using block chain? Trying to create positive brand sentiment in that setting is misplaced advertising. As the company fails in AI and cloud and block chain and ... the brand name will have much less residual value than the name B&H did because no one had a warm personal experience with it.