[Leon]

I can't help at spotting fake pennants too well but as for dating them, I don't think that will be extremely difficult on the ones that are from a bit later (post wwII). Many seem to coincide with an event which makes the dating of them fairly easy. If you really want to get into collecting them then putting your toes in the water with a few inexpensive, but certainly real ones, would help. I look at the sellers feedback and can get a feel, most of the times, if they are legit or not. Again, there will be those instances where good folks get fooled, but handling the most you can would certainly help. At least it does on the card side of the hobby. Maybe some others can chime in with a better idea.