Trying To Distinguish Between C138 And C138A By Tagging.

I am trying to identify stamp C138.

I have two singles and a block of four that has tagging over the entire stamp including selvage.

I have a pair that is tagged only on the stamp and not on the selvage.

I assume that some are C138 with prephosophored coated paper (solid tagging), May 30, 2001

I assume that some are C138a overall tagging, dated "2001", march 2003. Is this the pair that does not have tagging on the selvage?

I will see if I can attach a photo. It is 414K, easier to just push it to one of my libraries on my hosting site that is not even allowed to be mentioned. I will make the image smaller!

If that fails, I can resize and push it here.

Notice that the two stamps in the lower left of the not really in focus image have a different color tagging AND there is no tagging on the selvage. Initially I thought that there was no tagging but clearly the stamp proper has a different color than the selvage so I assume that is tagging. I am not so good with tagging.

I have a bunch of stamps I am trying to identify!

I agree with your tagging analysis.

Scott also notes a perforation difference:
C136: 11.25 x 11.5
C136a: 11.5 x 11.9
The easiest way to confirm the groupings above is to compare the stamps against themselves, rather than any gauge.
(Add: the shape of the die cut is slightly different most notabe at the corners.)

Interesting, I wonder how I had missed the perforation difference and the corner differences. I don't remember seeing it in my Scott catalog. I will take another look..

I did notice that the 2025 Scott catalog that I have shows variations that are not in my 2024. Scott catalog. I expect my 2026 catalog to arrive in the not too distant future.

Thank you for your very helpful analysis.

You are correct in that the first issue was on prephosphored paper where tagging appears Solid. Reprint C138a was Overall tagged. The apparent difference in tagging color is due to differences in the paper. C138 is printed on a non-fluorescent paper that appears gray under Long Wave UV. C138a is printed on a high fluorescent paper that appears a bright bluish white under LW UV. The high fluorescent paper makes the tagging appear bluish. In addition to the die cut differences John mentions, you can distinguish the tagging differences by looking at how sharp and clear the image looks under SW UV. Since prephospored stamps have the tagging printed over the taggant, The image will appear sharper/clearer and brighter. An overall tagged stamp has the taggant printed on top the image so the image appears muted and hazy/ not as sharp. See the image below.



High fluorescent paper can swamp out the green of the taggant especially if the overall taggant is not very dense. To verify if the taggant is present if its presence is in question, usually 10x magnification under SW UV will allow you to see the green taggant.

Also check out the tagging database on Stampsmarter.org for additional information.

OK, that is a lot to take in... I vaguely remember reading some of that previously but it was completely gone from my brain. Your photos show this very well and is very helpful.

I was not aware of the database, I will take a look.