There's a save state revision, when this number increases, the previous ones becomes incompatible (however, it's not a case of "every new development version becomes incompatible with the old one" like it is currently with the Shader Cache). The save state revision must be increased when something in the save state file structure is changed (e.g. accounting for an information which now requires more or less space to be stored in the file or having to store new info which were not required before, due an accuracy improvement in the emulator or a new feature). If the check didn't exist, previous versions wouldn't know what to do with the new data or with data that used to be of a different size, while newer revisions would not find the new data they are expecting since older revisions didn't store them. That would cause all sort of bugs and crashes...
Avell A70 MOB: Core i7-11800H, GeForce RTX 3060, 32 GB DDR4-3200, Windows 11 (Insider Preview)
ASRock Z97M OC Formula: Pentium G3258, GeForce GT 440, 16 GB DDR3-1600, Windows 10 (22H2)
ASRock Z97M OC Formula: Pentium G3258, GeForce GT 440, 16 GB DDR3-1600, Windows 10 (22H2)