I've got hundreds of rolls of 35mm (and some larger format) negatives going back to the '60's. They've all been stored in what were supposed to be good quality sleeved sheets in suitably sized ring binders. However, a couple of years ago, when I happened to re-visit some old holiday snaps stored in commercial photo-albums I was disappointed to realise that the colours had faded dramatically, despite reasonable domestic storage in a dark dry cupboard.
Time to drag out the scanner and regenerate the pictures, I thought, confident that I had well-stored negatives.
That was when I found that a lot of the negatives, (mostly Agfa), had also started to deteriorate. Whilst most were recoverable (just) some were too far gone to be any real use

So, I'll probably never know if the problem was bad storage or poor processing initially, but I do know that if I ever "get back into film" I'll be scanning the negatives at the earliest opportunity and making sure I've got at least two copies of the scans on different media!