Just read through OP, think you have done a great job with this! (Its the place I refer people to when Vanities are mentioned) though I have a little more info.. please read below

* The X-Ray Visor, Mechanical Man Helmet, and Squid Buddy have all been looted in D7 and Numa since the release of the Numa campaign. I have never seen any concrete proof of these three vanities dropping beyond Numa (i.e., in Slouch-O and SY).
Im going to throw a spanner in the works re. above statement (Trust that 'Canon') the person in question had a Mech Helm in the first day (or few days) of release SY! Not sure if it was stated what area but she definitely had her first Vanity drop. Please confirm with her, though im 100% sure it was in SY.

Quote Originally Posted by Defyduck View Post
Suggestion:-

I observed when i saw vanities droping it was the time just after the update and at that time all of us try to lvl as fast as possible so as i did.May be the chance of vanity droping is more when you play continous and regular.
Maybe another thought is that the probability of the vanities dropping are raised a little for new content. (Sneaky Sneaky)