Pat & List,
Yes they had a std plans book for MW. Yes some of the plans were the same as the PRR as alot of it was PRR and used the same plan numbers as the last book produced by the PRR. Now in the NYC & NH areas I would think that they also still used the former along with the new PC but they pushed the ex PRR influence into these areas under the name of PENN CENTRAL.
New plans were drawn as new items were purchased,sws, new & diff. wgt of rail,panelized sws,the need to chg older designs, etc. I have the front page which designates which numbers covered which group of items but I feel there are index pages which break down the groups for easy identification purposes as in the PRR C.E.13 or NYC or NH MW Std. Plan book.