Last summer I went to the Jamboree 2013 and got a few uncompleted Meritbadge blue cards. It probably wasn't the best year to do meritbadges there, but I wasn't instrested in the High Adventure stuff that was pretty far to walk to most of the time.
If I remember correctly, I was told I didn't need a meritbadge counselor to sign it off and I could work on it with the blue stamp on the card? There are a few meritbadges, like Railroading, that I know will never be offered to me again (and I don't know anyone who counsels that badge either). If anything, what does the blue stamp mean?
