Unopened FX-50 - still expired?

A year and a half ago I bought a box of Paterson FX-50 film developer (the environment friendly one - remember).

Two days back I decided to try it on a few rolls of T-max 100 from a nigh shoot.

The negatives came out very thin but still with some detail distinguishible.

When I developed another roll using my regular developer (HC-110) it turned out to have much more detail.

The question is: Is it common that developers in unopened boxes "go bad" like this one obviously has? Are certain types more likely than others (what about Xtol?) to perish.

FX50 was notorius for going off . I've tried Xtol too - that went off quickly! Rodinal is fine

Paterson devs do have a reputation as being short lived.

When the darkroom chems were temporarily discontinued a while back I bought in quite a lot of Aculux 2 (my dev of choice (and quite superb!)). Each bottle has a "use by" label which was good for about 18 months. We're now getting fairly close to that, but I processed a load of film a few weeks ago and it turned out fine.

Probably worth trying a low-value test roll first on bottles of dev bought a while ago (well, that's what I'll be doing from now on!).