It's not only medicals. We see it all the time with medicals, police clearances, and with requests for passports or travel documents. They're routinely asked for up front, at the beginning of a process, when in reality they're not needed until much later, certainly not until, if it's a marriage, a genuine assessment has been done.
It's only then that they would move to second-stage processing to look at admissibility. I can't see a reason why they could not hold off asking for those things until they're actually needed. Then there's a greater chance that they will not expire before processing could be completed. I think that would be an easy way to deal with it.
The visa posts have generic letters they send out with big long lists of stuff that they want everybody to come up with, including a medical, a copy of travel documents or passports, and a police clearance. They don't need it up front. They could just ask for them when they need them.