Limited share code validity

If someone’s share code expires in May, is it legal to offer them a 6 month AST in February?

They expect to be granted an extension (as do I on the basis of their status) but just wondered about the legalities.

Yes, you can offer up to 12 months

Thanks David. That’s helpful. I tried to find details of this on the web. Do you have a reference to some online doc on gov.uk or something?