Fork Lower Stamp# - What are they?

I have two forks lowers(see related thread "Caliper Mounts on KZ650 Fork" in this forum). One came off my 79 650B and I thought that one was original; the second was purchased as a replacement.

The original has "K207" stamped on it.
The new has "K723" stamped on it.

Looking at the parts diagrams for lowers on bykawasaki.com for 78-80, those stamped numbers don't seem to match what I have.

Are stamped numbers somehow different than part numbers?
How do I tell what I have?

Thanks in advance to the experts out there.

Those are called "Casting numbers" and have nothing to do with the part numbers. I have a set of what I believe to be 78 650SR forks in the garage, but I can't get to them to check the numbers or I would.