Interesting!
I wonder if it relates to the power-on vs power-off time?
All the old+good ones I've seen have been in industrial gear which is very rarely unpowered, or regularly off for only a low percentage of the time such as over a weekend, so the battery never has chance to fully discharge.
I have seen plenty of failed ones in equipment that has been taken out of service or on spare boards pulled from equipment.
They are obviously no longer on trickle charge, which is why I included the "permanent" clause.
I suspect the difference could be that with consumer gear such as TVs and computers etc., they are can be left to go flat at times and that causes the degradation?
Edit - Or, designers not bothering to check the spec for the cell type and using "1/10C" for button cells, which are the commonest backup type?
Those cannot tolerate that for long periods, if I remember right; they need a rather lower current with a permanent supply.