Extremely lucky. Would have been so easy (and even likely) for an old address to be unoccupied, or for the new occupant to simply bin it, or for them to put it to one side and forget about it until it's too late, and that's without even thinking about anything nefarious.
Honestly can't even comprehend how it's possible to forget to change the address on this. If I was moving, then that'd be the first thing I added to my "must notify" checklist, before Banks, family, etc.