Even those kinds of illegal magic that the Rathmores used to hide the Mirrorbound wouldn't convince the Watches that they've disappeared. They only stop functioning once a character is actually gone (dropped), so they'd still be working fine after escaping from that kind of cut-off situation.

As for the rescue: it's highly plausible that someone found the cache of stashed watches and gave his back very soon after the actual rescue. Returning stolen belongings definitely would have been a priority.