Rover owners: VVC head. Advice please

I have a second hand head that I plan to fit to my 135 along with 160 Pistons and liners. I began stripping the head yesterday to check valves etc before taking it to get pressure tested and checked over. My rear inlet cam has a chip out of one of the lobes that passes the camshaft sensor. I have attached a picture. The camshaft has 2 lobes at this position. The second lobe is fine.

Question is, what might have caused this? engine seizure?. I have ordered another set of inlet cams from eBay but looks like I will need to do the timing with the VVC units!

Attached Images