I'm positive most of the the cobalt bits we know of, are all pre-'71, when Michael Harris left and Jim arrived.
Marlene Bristow confirmed that my tricorn charger is by Harris, she remembered it.
I know John has a small cobalt piece by Harris, which came from Elizabeth's own collection of his work.
We do know, for certain, that Michael Harris worked from the cobalt pot.
Was there a period of overlap, with Jim being there before Harris left?
I am completely unconvinced that any post-Harris "dark blue" is related to the one cobalt pot of legend.

John's just posted a pic of the bit from Elizabeth's collection.

There are just a lot of different shades of blue that appear, later on; some are really quite deep.