The question was to see all of the units currently in service rather than one example of each.
From now over the next 12 months:
Liverpool Street - 315s, 317s, 321s, 345s, 357s, 360s, 387s, 379s, 710s, 720s, 745s
Yes, although you aren't going to see all the 345s at Liverpool Street until such time as the Crossrail tunnels are open as a) the fleet is split between east and west side operations and b) transfers of units are relatively infrequent. However, you have Paddington down for them. You also aren't going to see c2cs 387s at Liverpool Street. Agree with the rest. So we need to add
Barking (which will also help with the 4-car 710/2s in case not all of them cycle into the West Anglia allocation. Although 755s are possibly to be seen at Liverpool Street now one made its first passenger journey there yesterday, I don't think they will all cycle there, especially the 3-car variants. I suggest
Peterborough for this although
Norwich would obviously be more efficient if the only missing fleet is 755s. Also, even though Peterborough sees most of the units working on the lower ECML, you also need
Finsbury Park for the 717s.
Ashford International* - 171s, 375s, 376s(?), 377s, 395s, 465s, 466s
No 376s at Ashford. You also might not see the whole of the 4-car 171 or 465 / 466 fleet in a year. So I think we need to add
London Bridge
St Pancras* - 43s, 222s, 373s, 374s, 700s
I think this can be dropped in favour of
Nottingham where you will see all of the EMR fleet. Although the 374 don't stop at Ashford International, it would in theory be able to see them pass there on the main line.
Stourbridge Junction - 168s, 139s, 172s
Yes, this is necessary for the 139s. You will see the Chiltern 168s and 68s there but not its 165s so I think you need
Banbury which has the benefit of also covering the LTV 2-car 165s.
Ryde Pier Head - 483s, 484s
Yes
Clapham Junction - 158s, 159s, 378s, 442s, 444s, 450s, 455s, 456s, 458s, 707s, 710s
Yes, all of the SWR fleet can be observed at Clapham Junction together with the Southern 377s and London Overground's 378s and 5-car 710s.
332s have a matter of weeks left to work (and you won't see all 13 remaining units working). Paddington is necessary for the west-side 345s and, indeed the 387 fleet. However, we have been told on these forums that GWRs 769s won't go to Paddington (or Banbury) so I think
Reading is needed as well for them. Indeed Paddington can drop off in favour of Reading if you are content not to see the Heathrow 387s in service and 9-car 345s start running there again.
Cardiff Central - 67s, 142s, 143s, 150s, 153s, 158s, 170s, 175s, 165s, 166s, 769s, 800s
Yes, once GWRs 143s are withdrawn, you could take a punt on all of its 150s, 158s, 'West' 165s and 166s and Castle HSTs operating to Cardiff Central although I imagine it is feasible that the 150s won't all cycle there given their primary use is now beyond Taunton, so perhaps
Exeter St Davids is needed.
Leeds - 68s, 91s, 142s, 155s 156s, 185s, 195s, 220s, 221s, 331s, 333s, 801s, 802s
This should be good for a large amount of the Northern fleet although 156s are relatively rare at Leeds and you might need
Newcastle as well as
Manchester Piccadilly to see the whole fleet. Only 4-car 331s at Leeds at the moment.
Everything else in Scotland, around Manchester, and regional Anglia plus 230s and 313s
*Unfortunately Eurostar not stopping at Ashford Intl for the foreseeable future has forced me to include St Pancras instead of having 373s, 374s at Ashford and 43s, 222s at Leeds
You have missed LNRs 319s and 350s which you will need to see at
Bletchley to also cover the three 230s.
Chester is necessary for TfW's 230s and the Merseyrail 507 / 508 / 777 fleet. Also Avanti Voyagers
Manchester Piccadilly is necessary for Northern's 323s and the 3-car 331s. Also Avanti Pendolinos
Brighton is needed for the 313s.
Birmingham New Street is needed for WMRs fleets in the West Midlands that don't venture far - eg 323s and 170s / 196s.
Then, as already discussed up thread,
Glasgow Central and
Glasgow Queen Street to see the Scottish stock, although it may also be helpful to include
Edinburgh Waverley to speed up the sightings.
In reality of course, the best way to work this trivia puzzle out is just to identify the main depot for each fleet and choose the nearest station, then consider whether there may be points where more than one fleet can be seen.