I actually tried to find an answer to your question and ended up going down a rabbit hole so try and stay with my nutty answer. So in the Julian calendar the number 549 actually stands for a common year. A common year is a year that starts on a Friday. Now to make a long story short it turns out that 1971 was a common year and the first of the current era. So maybe the person who stamped your trans was as nutty as me or......they just used the wrong stamp. Now I need a nap I used up all my brain cells.