Posted By:
DavidI've never owned one of these suppliments. However, I'm aware of very few of these types of suppliments or premiums that were issued folded, and they would usually be of size larger than 8X10". If an issue was 'factory folded' it would usually be obvious by the neat and linear fold pattern. If as issued, it would be prudent anyway for the seller to mention that the print has folds so there isn't any confusion.
I know that the Baseball Magazine Premiums (unfolded), which can be quite large, were mailed in a jumbo padded envelope. The largest sized Harper's Woodcuts have a natural fold down the center, but these weren't actual supliments or premiums, but a printed part of the magazine.