In looking at the images of the two nickels lacking mintmarks, I wonder if it's possible that the photos are mismatched. The obverse of the 1944 and the reverse shown with the 1945 both look like Henning counterfeits, while the obverse of the 1945 and the reverse shown next to it appear to be genuine 1945 coins. I say this based on their color and the obverse lamination, both of which are typical of "war nickels."

You have unfortunately scrambled the images of the reverses of the 1944 and 1945 no-mintmark nickels:

You can see easily by the color: the 1944 nickels, made of Monel metal, look an even copper-nickel color, while the 1945 silver nickels are two-tone. On the 1945 reverse (shown as 1944 reverse), the mintmark (S?) is very faint and the E of E PLURIBUS UNUM is barely visible, while the M is worn off entirely. Since your closeup is of the wrong coin, it does not add anything to the discussion.

Your readers are astute; indeed, the reverse image on each should be changed. The 1945 reverse is after the 1944 obverse, and the 1944 reverse is after the 1945 obverse. Most likely my error, sorry!

I looked at the images and the 1944 is a "genuine" Henning counterfeit (weak detail on Monticello, copper-nickel color), but the 1945 nickel is a normal Wartime silver nickel, as you can tell by the color. I believe that I can see traces of the mintmark over the dome, though it is quite weak. (Take another look).

Regarding Henning, though, according to an article in Coin World August 28, 1968, p. 33, Henning is known to have made dies with five different dates: 1939, 1944, 1946, 1947, and 1953. (He was afraid that tellers might become suspicious if all the deposits he brought in had the same date.) No 1945 is known.

Of these, the 1944 is the most obvious because it lacks the mintmark and is the wrong color. But the others can be recognized too; this article illustrates one of the 1939 counterfeits. All the Henning counterfeits can be positively identified though weak reverse detail, rough surface, and (in some cases) diebreaks.

Not being a photographer, I spent time trying to get the best focused pictures as close as possible with my son's camera (digital, Sony, 5.1 megapixels). I think I see the barest shadow of a mint mark as well, though I cannot with my eyes on a magnifying glass, nor in many shots, but on some of them it does appear as though there might have been a "P" there, which seems so odd since the surrounding raised portions, though worn, are quite distinct.

When I look at the shadow, if it is indeed a mint mark, it appears to be off-kilter, either pointing to the U above instead of the B, or leaning to the right. It does not appear to be in the normal placement, or maybe I'm just seeing things.

I raised some similar questions about Henning/non-Henning nickels a few months ago at forums.collectors.com/messageview.cfm?catid=26&threadid=797202 .