London Victoria overnight Southern unit stable question

Hi! According to RTT three Southern services arrive at platform 9 London Victoria within short time at weekdays late night. Those are 2K71 ex West Croydon (23:37), 2I69 ex Epsom (23:47) and 2B53 ex Epsom Downs (00:03). All three are 8-car (2K71 and 2I69 are the pairs of 377s, 2B53 is a pair of 455s). There is only one departure to depot as 5T74 for both timetables (Dec'18 and May'19). Meanwhile there is only the one departure for platform 9 is 1L02 to East Grinstead prior the others arrive.
How it could be? What's wrong or erratic with it? Could 5T74 go to Stewarts Lane as 16-car formation off 2K71 and 2I69 joining though Southern's Victoria platforms can accomodate up to 12 cars. What forming 1L02 next morning off? Is there any sort of error or incomplete data in RTT?

I haven't got the stock diagrams handy, but there is no chance a 16 coach train would ever be booked to leave Victoria Platform 9*! It may be the case that the platform numbers are nominal and that the Carriage Working Notices (CWNs) vary on an almost nightly basis. Don't forget the CWNs for a station like Victoria are very complex and the slightest change results in many a ripple effect.

* In theory, you could probably still run 16 coaches from Platforms 18 and 19 on the Sussex side, although use of the full length tends to be restricted due to the resulting loss of flexibility, signal sighting, dispatch issues etc. I'd need to check, but I believe it's currently preferred that no more than 15 coaches occupy P19 and 14 coaches in P18, but you rarely get more than 12 in either, anyway.

2K71 (8x377) joins with 2I69 (4x377) to make a 12 car and goes down to Stewarts Lane as 5T44 M-T obviously Fridays are slightly different for some moves.
2B53 M-T (8x455) forms 5T74.
The complication comes with Stewarts Lane having some capacity issues overnight so to leave some breathing room for them, the stock for 1L02 0521 - East Grinstead (8x377) which works off 5T02 actually berths in platform 9 overnight at Victoria I think 5T44 goes to Stewarts Lane as a 4 car depending on inspections.
However as has been mentioned the platform numbers in RTT are only what is booked in theory and shouldn't be taken as gospel.

BromleyBoi said:

2K71 (8x377) joins with 2I69 (4x377) to make a 12 car and goes down to Stewarts Lane as 5T44 M-T obviously Fridays are slightly different for some moves.
2B53 M-T (8x455) forms 5T74.
The complication comes with Stewarts Lane having some capacity issues overnight so to leave some breathing room for them, the stock for 1L02 0521 - East Grinstead (8x377) which works off 5T02 actually berths in platform 9 overnight at Victoria I think 5T44 goes to Stewarts Lane as a 4 car depending on inspections.
However as has been mentioned the platform numbers in RTT are only what is booked in theory and shouldn't be taken as gospel.

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Interesting. Thank you! Could be this complexity to affect the maintaining of the right diagram's sequence? I mean, is it important whether the diagram B starting at early morning in depot or any station necessarily should be off the diagram A finishing previous late night in those points or should be off any other diagram forming the same type of rolling stock and carriage number? We aren't talking of course about disruptions, engineering works, stock's failures, short termed timetable but only about normal situation. These things may be not significantly important for such places as Victoria or Brighton with adjacent depots but may be important for e.g. Littlehampton, Bognor Regis, Eastbourne and its sidings where several units berthed overnight. Sorry if my question a bit unclear.

PS And isn't 2I69 a 2x4 377? Its diagram all day works at VIC-EPS-DKG-HRH as pair of 377s, isn't it?

The sequence tends to remain the same it is just solely ECS workings that tend to be affected. The stock retains it's diagram rotation just as mentioned minus the odd ECS, I can't comment about coastal locations as my knowledge is more orientated around the Metro area.
The stock that forms 2I69 is a 4x377 it splits earlier in the evening to form 1I58 & 1I60 both 4x377.

BromleyBoi said:

The sequence tends to remain the same it is just solely ECS workings that tend to be affected. The stock retains it's diagram rotation just as mentioned minus the odd ECS, I can't comment about coastal locations as my knowledge is more orientated around the Metro area.
The stock that forms 2I69 is a 4x377 it splits earlier in the evening to form 1I58 & 1I60 both 4x377.

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Great! Thank you!
But... according with RTT (from May'19 TT) 1I55 arriving at VIC divides forming 2I58 to EPS (front) and 1I60 to HRH (rear). The first finishes as 2S92 at WCY and ECS to Streatham Hill shed and 1I60 forms ECS to Horsham CS. So 1I58 and next services of its diagram remain by the pair of 377s.
Sorry for annoying -)