I have tenants in the same situation and the advice I received was that up to 12 months is fine (Limited share code validity) although David didn’t give me any refs for this. You will need to that their right to rent is extended when it expires (it’s a simply thing for them to renew it provided they do have the right) and keep a copy of this. If they no longer have the right to rent at the time, removing them is much more straightforward than the normal S21 eviction route if it comes to that.
I’ll send you a message with a helpful article from The Standard about this. If I link it here, it’ll go into a never ending moderation queue
Note to mods: please sort out the delays we face in linking to external sites