Hi Bob.
Yes. I have one the same, with the yellow sleeve, however it also came from a 140.
I haven’t seen any photos showing it on a 120 but I have seen ones with a corrugated sleeve over it albeit these photos were of early 120’s. Late 120’s I am unclear.
Regards, Graham.
Our “other Australian expert” in Jaguar XK 120 Explored describes that the original XK 120 cables were metal spiral with no plastic covering. Nothing about a yellow tag. No references found in Urs Schmid’s book nor in Porter’s version.
Hope this helps.