Gum

Nice stamps/pics!

The technical term is set-off (or setoff). Not unusual on early 20th century US flat plate printings. The ink is not actually on the gum, but on the back side of the stamp underneath the gum. On flat plate press printings, the gum was applied long after the ink dried. This is why you will sometimes find setoff ink on the back of used flat plate press stamps. Your 3 stamps do appear to be "natural" set-offs that happened during the production run. But hard to say for sure without physically examining the stamp.

If the ink is on top of the gum on flat plate press stamps, that is not production setoff, but damage caused by stamps being stacked/stored on top of each other under pressure in humid/hot environment. These damaged stamps are considered gum damaged should be heavily discounted by the seller, even if they claim it is never hinged (it's actually considered worse than hinged). If you don't care about gum, you can save a lot of money.

Set-offs are rarely found (although not impossible) on early 20th Century US rotary press printings. In this case, the ink is actually above the gum! Rotary press stamps with set-off on the gum are often considered a (minor) defect, but like straight-edges, that's really in the eye of the collector.

Stamper49, as per what hdm1950 stated, the landing gear is there. I also took my magnifying glass to it and confirmed that.

khj, the first local meeting I will attend is on the 14th. I was mistaken about it being held this past Tuesday. Hopefully, someone there can determine if the gum has set-off ink.