Fighters are classified by generation, as explained in this answer. Given this Wikipedia sum up, some fighters are not clearly in a defined generation, especially for 4th generation subclasses. Thus people may not agree on a list of fighters that belongs to a generation.

Some of the previous generation (generation 4, 4+, 4.5, 4++) are still actively produced (e.g. Rafale, F/A-18E/F) while the F-22 (definitely 5th generation) is no longer in production.

Airframe designed a long time ago (e.g. the F-15, F/A-18) still receive updates that make it competitive on international market (the section about potential operator of the F/A-18 on Wikipedia give an overview for the F/A-18), even in front of 5th generation fighters (at least in Canada for the F/A-18 and the F-35)

Another capability we cannot rely on to define generation is stealth. The A-12 and more precisely its variant YF-12 was stealth supersonic aircraft with weapons (AIM-47) inside internal bays, but was not a 5th generation fighter. Moreover, since ECM can be fitted on a fighter, this fighter expose some stealth feature.

Given those facts, it seems that since the 4th generation, knowing a fighter is classified as a specific generation does not provide information about its production year, its capabilities nor its competitivity in front of other nation's fighters.

What information does the generation of a fighter give? How useful it is to know a fighter belongs to a specific generation?