Prephosphored Vs Overall Tagging

I'm trying to get straight the difference between these two. Scott uses the term "Solid appearance" on the prephosphored. Can someone help me with differentiating the two? I'm working with a large set of stamps in the Great Americans series. I've attached a picture of 4 different blocks of 2177 (Buffalo Bill).

The blocks at the upper left and lower left are overall tagged. The other two I am uncertain about.

Checking my Durland, I found the following:
2177 ... large block tagging ... plates 1 & 3
2177a ... overall tagging ... plates 2 & 3
2177b ... solid tagging ... plate 1
So your block with plate number 1 must be 2177b.
I agree with the previous post that the other blocks on the left are 2177a.
I suspect that the large block on the right is probably 2177b. The overall tagging on this issue usually appears a bit "grainy" while the solid tagging appears very "smooth".
Added: One caveat. The 2177b plate block is the only one where the selvage is tagged as well the stamps. I do not know if this is true of all 2177b. If the tagging on the block at the far right appears smooth under UV, it is probably 2177b. But I would think that prephosphored paper would have tagging in the selvage ... which would make it 2177a.
Added: Think I've talked myself into making the block 2177a just because the selvage is untagged.

Good stuff. The right side block of 20 is P#2, so I assume it is 2177a even though the tagging has no graininess to it. I just don't understand what I can look at and call it a "Solid appearance" as different from Overall Tagging. Here are (3) block of 20's which includes the one shown above. I'm going to go through some other albums and see if I have some more. I want to find another that matches the center left. I see that it is a lighter color than all of these others, but Scott usually identifies color differences.

One other thing that I noticed is that the taggant color on the 2177b is a bluish green whereas all of the 2177a blocks have a yellowish green color. I checked my 2177 plate blocks (all 5 of them) ... 2177 & 2177a have the yellow green color while 2177b has the blue green. Unfortunately, I do not know if the taggant color is consistent across all 2177b. Or across 2177 and/or 2177a.

Yes, the one at the right of your first image is 2177a (overall tagging), just stronger tagging than the 2177a at the upper and lower left of the image, and all 3 in your second image are 2177a.

Prephosphored means the paper has the tagging applied before it is printed (under the ink) and the tagging runs the full width of the paper, so if you see an untagged stipe at the edge of the sheet it is overall tagged (but sometimes the overall tagging goes to the full width of the sheet, so you can't go the other way and say no untaaged edge means prephos). Overall tagging is on top of the ink. So, overall tagging makes the image look hazy under SWUV, while on prephos paper the image looks sharper under SWUV. Or you can get out a magnifier and look for the green glow or no glow on tp of the ink (but it is not easy).

The 2177b (middle left side) is printed on a low fluorescence paper which gives it a blue green color. Check out the stampsmarter tagging database for the different varieties. The others blocks above are overall tagged. If you use a 10x magnifier check an area where there is a larger patch of ink. If you look closely you can see the taggant on top of the ink for overall tagged stamps.

I use the stampsmarter tagging database quite a bit. Good call as it shows the blue green and the green. Maybe different types of paper were used. Thanks for all of the responses.

Yes, different paper was used. You can use a long wave UV (blacklight) to explore paper varieties.

Something more not mentioned yet, if you suspect Overall tagging (and preferably have some on selvage).
Note this effect is not so dependable or even possible on more modern issues (due to a combination of the overall tagging being a more recent formulation and what kind of printing being overcoated; e.g., gravure printing and/or glossy paper).
But on older issues like this one, up to mid-1990s say, you can scratch a tiny bit of the stamp with a fingernail, and scrape up a bit of the overall tagging and see it at the fingernail under short wave ultraviolet light. Just be sure to clean your fingernails before and after, as you might want to repeat with another stamp etc.