I guess I could take a stab at this.
Of the pics that I've seen of 256 cans, the embossed numbers appear rough-textured, as though they were part of the forging process, like casting numbers. Possibly a way to track the forging operations, or to indicate a change to the raw forging.
The follow-up machining process is independent, and can have its own variations.
The 256 cam appears to have possibly 10 variations, since it started with part number suffix -00 with the '70 XS1 to early '71 XS1B. The suffix was bumped to -01 with the mid-year XS1B, possibly to correct a grinding error. The final suffix is -09, to be used as replacements for all 256 '70-'73 engines, making a possible total of 10 variations. The variations could be simply improvements in the grinding process and tolerances, and/or supplier changes, similar to what I witnessed on Hondas. I haven't seen suffix numbers stamped on the cams, and have seen only one document about a 256 cam change, to cover that grinding error.
I've had my suspicions about secret/undocumented cam profile changes, similar to the different cams used on the Honda CB350 vs CL350. Very subtle timing differences to move the torque peak high on the CB, and mid on the CL, and to match the different exhausts.
This *was* done when the cams were changed to the 447 version.
Honda kept the parts and service departments informed of this, but not well revealed to the general public. Back then, Yamaha's documentation and parts revisions were not up to the same level as Honda, so these cam markings may simply remain as mysteries.
Edit: In addition to the mid-year '71 XS1B camshaft suffix number change, 2 other changes concerning the camshaft occurred.
- Change from internal roller bearing to bushing, for the advancer shaft.
- Change the 40x25mm end seals.
It is unknown if all 3 changes occurred simultaneously...