crippled veterans

[M. Caecilius]

There are passages about crippled soldiers complaining about being keep in service BEYOND their required service time.

Are you referring to Tacitus, Ann., 1.17 - in the context of the mutinies after the death of Augustus? If so, this would show that such practice did occur, but was not seen as acceptable (after all, it contributed to a large-spread mutiny). Tiberius and his agents seems to have been fairly effective in calming matters. Though I concur that it's likely that such practices were not ended once and for all and that such situations would have repeated itself often enough to save money.

Gordian's rule of a "competent judge" deciding whether or not a soldier would stay might could be used to support your suggestion. Such a person could quite well have decided that a soldier was maybe not fit for service in the thick of battle, but could still work in the fabricae, look after the draft animals, work as a messenger or with the catapults, depending on his wounds. I guess it would depend on whether the soldier walked with a limp or had his leg amputated: perhaps checking the medical writers (Celsus, Galen...) would be worth a try?

It would also depend on the question of why Gordian (or, if he re-affirmed the rule rather than innovated) regulated for a tight examination. Was the army desperate to keep people (who were trying to get out under any pretext), or were the soldiers trying to stay on receiving the benefits of legionary service (or avoid potential life as an beggar after being left without pay) despite no longer measuring up to a high standard? Could the Roman army afford to discharge people who could still wield a sword? The passage from Tacitus seems to suggest that, at least occasionally, the army was pretty desperate to keep up its numbers; at other times, it may have had more of a choice to keep up to an ideal standard as proned later by Vegetius.