All 1970-D are large date. Notice the tail of the 7 extends lower than the 0. 1970-S are the only known small dates.
There are a couple a marks on the tail of your 9, any curving is probably PMD. This is a well known variety, if there would have been a small date in another mint mark it should have been documented by now. Of course there can be a first, but yours is normal.
I understand what you are thinking. So consider this, the 1990-D cent mint mark. If: In 1990 and 1991 the Mint began applying the mint mark to the master die for circulation strike coins. After 1994 the mint mark was placed on the master design. A major turning point for hub and die production in the U.S. Mints came in the summer of 1996 when the Denver Mint opened its own die making shop. Prior to this, all aspects of the die making process were done exclusively at the Philadelphia Mint. The new Denver die shop was equipped with the single-squeeze hubbing presses that the Mint started developing in the mid-1980’s. And: Is it possible that a working die meant for 1990 Philadelphia production was altered to be used at Denver? Could it have the MMS-012? Or, .... the MMS- 13 in a different position? It’s always good to ask questions!