To be honest, it's like pulling teeth trying to get the true facts surrounding the circumstances of re-entry - an evasive individual starts alarm bells ringing.
If the individual physically joins, swears the Oath and Attests (signs-on), then is discharged, they are classed as an untrained re-entrant and require approval to be processed - based on their former service.
If the individual is discharged and sent home before physically "signing-on", they can apply without the need to get approval but must still be passed fit to enter and pass all expired elements of selection - Including re-taking the recruit test if they have not already scored high enough for their chosen branch.
If the plates went in before joining & were not declared at the AFCO medical, then any subsequent injury is entirely the fault of the individual. If it was declared upfront & the injury was attributed to training, then they must be passed fit before eligible to rejoin.