The 1912 nickels of all three mints tend to be a bit mushy overall, with sharp strikes being quite rare. Since the proofs are quite sharp, this deficiency was probably not in the master dies, but it may have been that some of the working hubs used to make working dies were not fully impressed.
This date is plentiful across all grades.
Mintage:
Philadelphia | Denver | San Francisco |
26,234,569 | 8,474,000 | 238,000 |