Until the postwar period it was not so easy to differentiate between MO and Conservative. They were often interchangeable and the some clergy and regular members easily shifted between one and the other.
The big postwar break came with Conservative officially started allowing things like driving on Shabbos. They tolerated that and worse for decades until then, but that’s when they started officially justifying it with pseudo-religious arguments emanating from their Rabbinical Assembly.
While the RCA reversed itself on using microphones on Shabbos and didn’t officially permit driving on Shabbos or open gender seating in shuls, the reality was even until the 21st century some OU Shuls had no Mechitza and some even had open parking lots on Shabbos, even if the latter at least wasn’t officially condoned, it was certainly tolerated with a nod and wink. Avi Weiss’ synagogue is still an official OU Shul till this day.