Winchester Model 63 operating sleeve ( plunger ) installed upside down from the factory|Winchester .22 Rim Fire|Forum|Winchester Collector

I would like to know if anyone who is an expert on Model 63’s could answer a question I have regarding my late Uncle’s 1958 Model 63 with grooved top receiver, serial number 173,283. It has the operating sleeve ( plunger ) with the notch in the bottom of the fore end cap and not on the top, as all model 63’s have that I have seen other than his. He bought the gun new in 1959 at Phillips Sporting Goods in Great Bend, Kansas. I have pictures to prove it came this way. Does anyone know of similar Model 63’s with the fore end cap slotted at the bottom and not the top? I can’t think of any reason the Winchester would alter one rifle on the assembly line in late 1958 ( per the serial number ). Thanks for any help with this question.