Further to this comment, it is now apparent that the 9-car workings on the east side are formed from units based at Old Oak Depot. Therefore, the units now carry maps for both the west side and east side operations. It looks like there is effectively a three day cycle for 9-car units working on the east side, going east during the day on day 1, working an evening peak working, working all day east side on day 2 and then returning west after the evening peak on day 3. Obviously, service perturbation can affect this pattern. Not long enough yet to work out whether there is a distinct subfleet of these units.
Although west side 9-car units work through the tunnel to get to the east, a distinct fleet still seems to be in place for tunnel trial running. Interestingly, recent 9-car conversion 345010 appears to have joined this fleet instead of going out on west side workings. As an example from yesterday, 345010 is implied to have been on one of the trial running diagrams.
View attachment 97386
[Picture shows a screen shot of output from TrackIt! with headcode '5I10' reported cancelled at berth C313 having returned from Paddington (Crossrail) on 5Y74 2005 Paddington Crossrail to Old Oak Depot around 2013 on 31 May]
The attempts to get 7-car 345042 back to the east side last week appear not to have gone to plan - it looks like paths are in for another go tomorrow, with another potentially going in the opposite direction.
1026 Old Oak Depot to Ilford E.M.U.D.
https://www.realtimetrains.co.uk/service/gb-nr:K02062/2021-06-02/detailed
1517 Ilford E.M.U.D. to Old Oak Depot
https://www.realtimetrains.co.uk/service/gb-nr:K04506/2021-06-02/detailed