All 'block booked' tickets have the respective 'block bookers' reference number printed on the tickets. Plus ticketmaster tickets are completely different.
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The ones they were selling in the Carroll's shops in town looked the same as block booker ones. They'll know from the seat numbers if they're elligible for tickets anyway.
I sent 2 tickets in one envelope... The other ticket is my brother's which I stated so that should be alright, I hope...