Re: Lancaster varients
 

Sure, yes. Correct, possibly not, it seems! My opinion may have been excessively influenced by later usage.

I have three manuals: All are titled without the use of Mk.
The Halifax III is referred to as such throughout, and similarly its Centaurus engines.
The Spitfire V is similar, but includes such use as F VA, LF VC, etc, and similarly its Merlin engine.
The Hurricane II is titled, and begins, similarly but the second paragraph of the Introduction refers to the Mk.IIA, Mk.IIB and Mk.IIC. This might suggest that the Mk. is only applied to subvariants, but in Section 1 Introduction there is "Hurricane Mk.II and IV". Not, you note, F. Mk.II. Possibly because no Hurricane was anything other than an F, so there was no need for any distinguishing prefix.

I suggest this tells us that the terminology including "Mk." was in use at least as early as April 1942 (Hurricane Manual AL 20), but that it wasn't considered critical, and previous habits continued even in official documents. Which would also apply to the absence of the prefix on the Hurricane documents, of course.

Edit. Move it back six months: Some years ago I was shown Bob Sikkel's notes on the origins of the prefix. I shall select from the documents he quoted, without hopefully distorting his meaning nor spoiling his hopes of future publishing. In meetings held in October and November 1941, the matter of the correct way to refer to the PR Spitfires was discussed. A replacement was needed for the "Type D", "Type F", "Type G" terminology. It was decided that the new terminology should be PR Mk.1, PR Mk.II, etc.

Note that this meant the mark numbers started at one for each role prefix: something that can be seen in the PR Spitfires, the Seafires, the TT Defiants, and the Trainer Fireflies. Further discussion for the Mosquito lead to the modification of the system, wherein the mark numbers were issued in sequence and more than one role prefix could be applied to each mark: thus B Mk.I, PR Mk.I, NF Mk.II and T Mk.III. Note that the Firefly Trainers postdated this change.... the well-known changes to the Seafire and PR Spitfire Marks show that the system continued to evolve.

The point I take is that use of the full official terminology predated November 1941. Although even these documents, let alone others, continued to use incomplete references (e.g the mention Spitfire Mk.VIII or just Spitfire IX) the full terminology was in place.