I'm not sure when it change but I know there are RI buttons with the fouled anchor with the backmark GOODWINS PAT. JULY 27, 1875. I'm thinking they probably changed shortly after that as there are Span-AM RI buttons with the unfouled anchor.
You're welcome. Most of the later buttons with the unfouled anchor are really plain looking next to the earlier buttons. I don't know if anyone had ever noticed but the detail on most of the civil war and earlier buttons is a lot better than that of the
Span-AM & Indian war period buttons