The white star would have been there from the factory, the Americans were very keen on painting them on there. It recently
came up on Missing-Lynx that the British ordered large quantities of American OD paint in 1943, most likely for touching up American vehicles. Chances are, I would say, that they used some of that to overpaint the stars on your tank. But did they then paint the 17-pounder modifications with that same paint or with British OD (=SCC 15)?