The one I've got here with the loader has a blank decal too, the decal is clean and undamaged but blank.
Where the numbers stamped or printed on these decals? Maybe they got wiped off over the years?
I checked the parts pile and I've got four other panels with model numbers here from the last estate lot and none of those decals have any sign of number on them either.
Those labels were printed and the printing wore off over the years. Sometimes, like Jerome suggested, you can wet them and in a raking light you can see a ghost of what was printed on there. Other times, not so much.