Alas, no. They ignored the markings and life continued as usual. Two weeks later, we got the old stubs (jcobleigh's was forwarded from his old address by the Post Office). I called them, told them all the new information, requested that they consolidate our contributions on one stub, etc. They assured me that everything was set.
Nothing changed, except that they sent my stub to jcobleigh's old address. It's probably languishing somewhere in his landlord's mailbox as we speak, since the Post Office hasn't been instructed to forward mail addressed to my maiden name to our current address, only mail addressed to jcobleigh's name.
So we called again today, badgered the person on the phone a bit, reiterated the information, and insisted that they read it back to us.
We will see if this has any useful effect whatsoever.