There have been instances of mature products, that were produced and performed reliably for years, suddenly becoming unreliable because a component provider improved their product to run faster. Since the parts were specified with just a minimum transition time, the newer faster parts easily met spec. But since the existing traces were suddenly well over the new critical length the circuits just weren't reliable anymore.

Seen that one, a typical result of 'testing' rather than 'designing'. If you do not design to work with signals propagating at the minimum time given in the datasheet and all chips you 'test' with at that time are running close to max you will have a terrible design and a very succesful test. Then, when you thingy suddenly fails a year later, go up on your soapbox and cry "irresponsible manufacturers" NEVER blame yourself, that the later chips ate still perfectly within that specs in the original datasheet is, of course, not your concern.

The above reflect very closely the readction of the 'designer' of the thingy it took yours truly and another (better than me) engineer a VERY long time to solve (the error signal was narrower than what that days available scopes could show, we had to 'mentally scope' every darn signal in that unit). The problem showed up as a 'hit' once a week.

Erik