It was the curtness of Kevin's original post that had me confused. I understand the special printings quite thoroughly. Not sure why a mountain got made out of a molehill.
Let's move on. If a picture is worth 1000 words, here is a picture lifted from
ebay, showing a full sheet of 200 of Scott 758. The stamp starting this post is cut from the lefthand column of a similar sheet, (although not the 10th or 11th stamp down, since those two positions would show the arrow).

The presence or absence of gum is not a 100% indicator, since imperforate sheets of the National Parks could be sent in for gumming, and conversely, singles cut from the souvenir sheets could have lost their gum over the years. So gum is not so simple. Fortunately, yours is identifiable from the front due to the selvedge as already noted.