After the fact, it is extremely unlikely. The University almost always state that MCs should be submitted at the time when the event affecting studies occurs. It is incredibly difficult to get retrospective MCs accepted, especially in a final year when it potentially affects whole-degree classification. THings are a little freer with resits, but again, in terms of retrospective MCs the odds are still quite long.
If there are prior MCs, then these have already been applied and should in theory have no further role in terms of grading and thus in terms of classification. It'd need to be a new claim.
At my place we are (only just) still in the assessment period. Your boyfriend needs to speak to the MC team/student support/personal tutor/AA as a matter of priority if there is even the slightest sniff of mitigation being granted. The odds are not in his favour, but that doesn't mean that he ought not seek counsel about it.