Top Fork Bush question

I have been messing with Commandos for 40 yrs, but this slipped by me. I recently bought new bronze fork top bushes, and when removing the old ones, noticed that they had grooves (3-6-9-12) cut in the brim of the bush, the new ones did not. I just can't remember if this was a proper mod or what..any clues? Thanks.

Mod, added so oil is retained.