I've been trying to update the Claim Number on gifts we've already claimed and received Gift Aid from HMRC from, but which are now beyond the eligible claim period - it's retrospective admin jobs I'm doing.
Unfortunately the only way to do this now is to change the system date.
If only there were a simpler way of overruling this constraint.
If you have a list of the Gift Import IDs you can update the Tax Claim Number field by importing it, even after the claim window has passed.