Need help finding serial numbers on Mamiya RZ lenses

Im trying to locate the serial numbers for several Sekor Z lenses that i own, but i can't really seem to find them. There is a sticker with two letters on the lens mount and a 5-digit number next to where the lens information is on the front element. I'm hoping someone can help me find the serial numbers for these old lenses because i cant really seem to find them on my own.

I don't have but one in front of me, the 90mm f/3.5, and the serial number is on the front of the lens body, where the lens specs are engraved. There's a five-digit serial number counter-clockwise from the top orientation as you look down on the lens, apertures, D-O-F, etc.

 

I looked on eBay, and most of the ones I saw had the serial number in the same place.

 

The serial number won't be attached using a sticker. To my knowledge, they're all engraved.