Sc751 Or Sc769, Gum Or Not?

I have this stamp from the 30s, how could I know if it is an SC751 or an SC769, I know that the difference is in the gum... I see this one very clean compared to other similar ones, does this mean that it is an SC769 or could the gum disappear without a trace? Maybe expert eyes can appreciate it... Is there any test to determine if there is glue or not?

The stamp is cancelled at the bottom and subesquently soaked. Trimmed as it is, there is no way to tell of its origin of 751, 756 or 769, thus it would have to classed most generically as a 756, cut from the standard imperforate Farley sheet, rather than from the souvenir sheet..

Add: singles of the 1 cent and 3 cent Parks issue are problematic. One really needs pieces with selvage, guidelines or multiples to be able to positively ID them.

This appears to me to be a used stamp. So there should be no gum. Moreover, besides 751a & 769a, you should consider 756 (single imperforate stamp from sheet of 200). I actually think 756 is the most likely choice.

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