Adam Clarke on John 12:3

Then took Mary a pound of ointment - See the note on Mat 26:7; see also Mar 14:3. It does not seem the most likely that this was the same transaction with that mentioned above. Some think that this was, notwithstanding that before is said to have been at the house of Simon the leper. The arguments, pro and con, are largely stated in the notes at the end of Matthew 26 (note), to which I beg leave to refer the reader.