I had one from every show I went to, but then the earliest ones I had were ridiculously small, so I sold them on eBay. I was a little surprised how little they got though, considering they were all originals and in great shape
The oldest one I still have now is from Counterparts with the three monkeys
My favourite is the new uber soft 'vintage-looking' first album shirt that I got when i ordered my VIP tickets. Fits me well, looks great and is soft and cool.
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Postscript...My Iron Maiden shirts from the same era sold for well over $100 a piece when I put those on the 'bay