Seems that the phrase "X" List is associated with DMDs. The categories seem to have a "criteria" involved ;
1 - Price
2 - Availability
3 - Playability
4 - Visual presentation
5 - "Keep up with the Jones'" - ability
I think that this was all developed years ago by US collectors and Dealers. This has become some "pseudo standard" by which we rate DMDs. (Not all DMDs represented)
A List - MM, CC, AFM, MB
B List - TAF, TOTAN, ToM, CV, SS, GNR, Spiderman, IJ, ST TNG, CFTBL
C List - Dr Who, Shadow, Corvette, Roadshow, Junkyard, JP, Shrek
D List - Congo, Indy500
Of course there are many more titles. When you look at the categories, there seems to be a "leaning" towards Price.
Looking at that list from an "Availability" point of view, it might look like this ;
A List - MM, CC, AFM, MB, CV
B List - Congo, Indy500, Junkyard, TOTAN
C List - Shadow, Corvette, ToM, Roadshow, Dr Who
D List - TAF, IJ, Shrek, CFTBL
From a Playability point of View (again - my opinion)
A List - CV, SS, TAF
B List - MB, Junkyard, Shadow, ToM, CFTBL, AFM
C List - Corvette, Roadshow, Dr Who
D List - Congo, MM, CC, Indy500, ST TNG, IJ
I believe Price should be removed from the "X" List criteria. The main reason is because there is no "standard" for reconditioning or restoration - everyone has a different opinion on how it should be done.