Many thanks for your reply.
It still leaves the question of how the corruption(s) occurred and in which database. I can edit and save the contacts in my own Contact database without problem, and we can edit and save any of the pre-existing contacts in my wife's Contact database without difficulty. The problem occurs only with contacts sent by BBM, after they've been sent, which seems to suugest that BBM is introducing the problem. (We have the latest version - 126.96.36.199.)