The Vox Bassmaster didn't change too much over the years, and this parts list, printed by the Thomas Organ Company and issued to American dealers in March 1966, covers models made in all years. Bassmasters had been in production since at least 1962, although few were imported into America initially. The Bassmaster was only built in the United Kingdom; and instruments sold in other countries were all imported from Britain. It was not one of the models chosen to be produced in Italy, although a very similar model, the Vox Panther was.
This parts list mentions two different control knobs for the Bassmaster, the white plastic knobs that were the standard in the UK, and the knurled metal knobs (part 09-141-0, as opposed to the more widely used 09-314-0) that were not usually fitted to Vox's entry level guitars. Perhaps these knobs were being fitted to American imported Bassmasters circa 1966? The white plastic knobs were still being used in the UK at this time. By this point Bassmasters were not selling in large numbers either in Britain or America.
Follow the links in the document, to see further details of individual parts.