Lets try and second guess what might happen with the 397s. I reckon that the Anglo-Scottish diagrams from 16 December are the following:
Note that overnight stabling of the TPE trains in Scotland moves from Corkerhill to Polmadie from the December timetable change.
In the first week, Diagram H starts at Ardwick (5S30 0440 Ardwick T.M.D to Manchester Piccadilly) and Diagram E (5W67 0145 Manchester Piccadilly to Ardwick T.M.D) ends there. Also, 1S85 terminates at Carlisle and 1M90 starts at Carlisle. This is all unwound for the first week in January when the schedules indicate all units are at Longsight (3 units), Polmadie (2 units), Preston Carriage Sidings (2 units) and Glasgow Central (1 unit) with nothing scheduled off Ardwick.
On the Liverpool workings, there has been some indication in the Railway press that 185s will work initially with 397s favoured on the Manchester services. This appears to be consistent with two empty workings to and from Manchester.
Diagram 9 appears to end with 5J81 2111 Preston to Manchester Victoria and there is also a 5C89 2334 Ardwick T.M.D to Preston suggesting 185s.
These run until 14 February at which point there is a change to the diagrams with the introduction of interworking between the Manchester and Liverpool routes.
That would appear to mean that there can be, at most, 6 397 diagrams from the timetable change in December, but 3 (A,B,C) appears possible if Polmadie isn't ready. Given there are only 2 at present, this seems pretty tight.
It looks like there might then be a step up in the new year and another in mid-February, the same day it appears that the number of 68+Mk5 diagrams appears to increase so maybe 10 397 diagrams from 16 February.
Of course, substitutions by 185s and 350s are easy in the short term by simply sending units from Ardwick instead of Longsight and once they are in the cycle, won't be substituted by 397s - guess it depends on how quickly 185s go off lease.