It was the basis of the updates, subject to his future decisions.
He later removed the milled penny (that I recently sold) from the catalog after receiving an assessment from the Royal Mint that it was a post mint alteration.
Just as his 1970 edition was an extension of his several updated versions of his penny studies expanded to include half pennies, farthings, patterns, trials, etc.
There are ALWAYS corrections, updates, modifications, etc to a work of this magnitude.
There have been many new discoveries to add to Peck, Braman, Freeman, etc. No guide/catalog is a final authority, it merely contains information known at the time.
They grow, mature, learn, make adjustments and corrections, expand as a living being.