Yes u r correct.
ER maintains all its coaches very well. If u see old coaches of ER used in passenger/ mail/ express trains r quiet well maintained. If u see the pgr trains from RPH, MLDT , etc sides r quiet old but maintenance is very good although many r now converted to MEMU there. But SER on the other hand has very worst maintenance, all RSA done everywhere so rakes get very less time for maintenance and so very poorly maintained. If u compare RAJDHANI exp rakes of ER which has 2005, 2006 coaches very well maintained, on the otherhand SER Mumbai Duronto exp rakes has 2016, 2017 very poor maintenance. SER gives new coaches to Mumbai Duronto and...
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use them for few months or say 1 year after it gets old those coaches are given to other superfast trains and replace them with another new coach and cycle goes on. SER only does technical maintenance of brakes, etc in CDO interior and exterior cleaning not done. Another main problem with SER is SER has only 1 Workshop at KGP with huge pressure on it. ER on the other hand has 3 Workshop at Jamalpur, kanchrapara, Liluah so POH of coaches done is good.
I am telling you till 2017 SER had acute shortage of coaches specially in TATA CDO, HTE CDO, ROU CDO. We have written several communication to RB, RM to provide coaches to SER but RB used to allot less coaches to SER and many coaches which was despatched from ICF, RCF is on the midway gone to other zones. New coaches that came few in number were given to SRC CDO as due to poor maintenance many coaches wanted repair frequently in SRC CDO. As KGP Division is the major passengers carrying division in SER compared to RNC, CKP, ADA Division with many popular trains so few new coaches that received given to SRC CDO on priority basis. I tell u there was situation in TATA CDO that coaches from one incomming train is destached and added to next some other train that is to start journey from TATA. Now situation is quiet OK. But TATA CDO, HTE CDO, ROU CDO has many 15 to 25 yrs coaches that r used in many running trains so SER finding hard to find 329 coaches for conversion to isolation coach.
SER is using many GS coaches to conversion to isolation coach so maybe many Conventional passengers trains can run with reduced coach composition or may get cancelled also after train operation starts.
I think 329 coaches is quiet high for SER as SER is not a mainly passengers carrying zone like ER, SR, etc. ER is mainly passengers carrying zone and has many passenger coaches and 338 coaches for them is less but 329 coaches for SER is quiet high.

I don't think so
See the padatik express coaches
All khichdi coaches
Kabhi humsafar
Kabhi Duronto
Kabhi...
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Rajdhani
Padatik Ka ek rake sdah rajdhani ke purane coaches use karta hai
Kaziranga ke do coaches Ka livery jaise black ho
Kuch Kuch AC coaches bhi black livery type ke hote hai
I don't have much knowledge about HWH,ASN,MLDT CDO but SDAH is worst
Even it's EMU are very much and looks pathetic
Poorva ke GS coaches ke toilet windows humesha Nahi rehte hai
I have many heard that some coaches' charging point doesn't work