Over here is USAicon . The powder is Win 231. I do not know the load data for 146gr round nose , but for 148 gr WC , max Bullseye is 2.7 for 748 and Unique is 3.4 for 747 . If you up'd them to 4gr and 5.3 gr without knowing what you were doing , you'd be heading for a world of hurt.
It's kinda like the high speed 38 special ( 38-44 ? ) that came out just pre-.357 Magnum . It was in a .38 special case but made for the N frame ( IIRC) type guns . If you put them in J frame type guns , you'd have problems.
The 38/200 is to the .38S&W the same as the .38-44 is to the .38 special. So , yes , any 38/200 pistol can easily shoot any .38S&W load , and yes , any 200 gr bullet can be loaded to be safe in any .38S&W pistol.
It's just that the Victories and Commandos were chambered and marked for .38S&W and barreled to Americian specs. and someone in Britian realized this and erred on the side of caution.

Do you remember those square cement block things the used to make the artifical harbors after D-day ? They had pumps to pump the water in and out. One sole person claimed that the pumps would not do it. Everyone else thought he was crazy and an alarmist . On officer finally listened and demanded a test ( there had not been one ) . The pumps failed , so all had to be changed. If not for the lone voice , the Mullbery's would not have left Englandicon.

Chris