I don't have the link, but I have read two or possibly three cases on this forum where at the discretion of the IO the medical expiry was extended so the person could land without having to re-do the medical. That's why in the manual it says "validity is normally 12 months", which means it can be extended, or shortened if they feel like doing that. I imagine if a person goes to their interview and is hacking coughing like they have TB, the IO can also demand another medical done sooner than 1 year.
I think it's worth asking about at your interview. If there is one thing I have learned during this process it's that no two visa offices are alike, no two IOs are alike and no two cases are alike. The IOs seem to be able to do whatever they please, in whatever time line they please!