R168 10-Cent Battleship Double Transfer?

I posted this on my website yesterday, interesting to me because it's a combination of U.S. and Great Britain revenue stamps (mixed usages are fairly scarce), sadly not a complete document.

An eagle-eyed collector pointed out something I had missed, something going on in "SERIES OF 1898". I looked closer and sure enough, there are some lines of shading across the tops of the letters. None of the other examples of R168 I have scanned have this anomaly; the letters are clear at top.

Nothing like this is contained in the Shift Hunter Letters.

So, inking/printing anomaly or double transfer?

The cancel on the Battleship is "Strong & Trowbridge Co.", a New York export house.

It's a DT. It's also in the background lines above the letters of documentary (they run into the letters), and also the bottom of some of the letters themselves. It might well be in the flowers in between as well, although I would need a comparison example to be sure of that.

I don't have a lot of examples of R168 scanned. Here is one (hyphen hole vs. roulette notwithstanding):