The number 1 main bearing is supposed to have a champher on the upper shell. It is for timing chain lubrication. Except for the champhor the bearing is the same as the #2 and #4
Many if not most of the after market sets do not have the champhor. If I get a set like that I file the champhor on the edge of the bearing shell. I don't know about the aftermarket bearings, but the factory replacement bearing have that marked with a red paint mark.
PS: the factory service manual refers to this.
