I also resurrected my NHS number from 1992 which was when I last lived here. Was very difficult as my surname has changedI’ve resurrected a long dormant NHS number and am waiting to hear whether the local GP practice will accept me. There is the option to register as a temporary patient for a stay of under 3 months i.e. you don’t have to be a resident and show proof of local address.
Hope you manage to get registered.