I have 2 Fidjis as well. One purchased at Barneys last year and one from Bergdorf this year (went a little crazy when they were discontinued) and both have a serial number stamped on the underside of the leather tag at the inside top. It is formatted like yours, aileen_24, with 3 letters and 6 numbers. The codes are identical except for the last two digits; I have no idea how to decode a Goyard stamp but I would imagine the last 2 differentiate the colors.
Hope this helps!
Yep, they are quite hard to decode, and there's not a lot of info available out there. The 2 bags I have have different colors. One is magenta/hot pink and one is purple. I actually panicked when I received the magenta bag (pre-owned). I have not seen this color on a Goyard before (I thought it was light pink). But when I came here looking for answers, I found out that Goyard came out with the color years ago and discontinued it.