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I believe you, and I know it's not a good feeling when we notice this mistakes. I'm a designer and I've worked for many years in advertising and this happen from time to time, and there's only one good decision to take.. is to replace the material with a new and correct version.

You don't have problems regarding expenses because you've make MORE than enough on this post to cover all expenses to reprint all the flyers, stickers and t-shirs.

I'm giving this comments not to bash you ok? I'm just trying to help you make the best work you want to do, and I think you'll feel better in the future after the reprint, because then you'll know that what you're promoting has no mistakes.
Cheers, and hope to see new version soon! @fogspam

Tomorrow I will do this and I will go for next step. Lets hope other people with bigger companyes will do the same and start a chain reaction. This is what I am planing to see.

Best of luck ;)