There’s something about old flats that gets better over time.
Not quite the same but I changed the Cobalt flats on my stingray recently. The originals are a very old set that have been on a few basses. Pretty chewed up at the pegs but stable. They sound incredible on the MM but curiosity got the better of me so I changed them and out the old ones in the bin.
I’m not sure if the strings have changed but they didn’t sound anything like as good as the old ones. The old strings have tons of top end still despite their age and sound more like dead rounds. The new ones look and feel different.
As my wife came home from work she found me fishing them out of the bin! Put them back on - perfect!!