Flap sets 2S17 and 2S18
The Blue Book lists 2S18a and 2S18b. The Blue Book shows a sample 2S18a, but no 2S18b. Randall Holden sent the following information about the 2S18a,b flaps; "Another typical MVE (thick/thin 1919 1994) designation rather than a/b
varieties. There are too many of these where you need both to see the differences. Note: this is easier to know the differences than some of the others listed."
Randall's comments appear quite reasonable. Instead of listing 2S18a,b, it would be better to lists 2S18 (MVE), minor variations exist. It is possible to see differences in the 1919 and the 1994, but you must look very carefully. This is clearly not a signifigant change in the flap theme.
The same comments apply to the two 2S17 flaps. Here the Blue Book lists the single flap, 2S17. However, look very carefully and you should be able to see that the Sanhican and WWW are thick on one patch and thin on the other patch. This is another example of MVE.
David Oertle writes about the 2S18
"If someone has a S18b I'd like to see it. Here is the true story how it got listed (by mistake). I was visiting Bill Topkis in Utah about ten years ago. Jeff Morley was there too. Topkis was then Blue Book Editor. I brought two flaps along which I suggested could be S17a and S17b. I have had more than one of each. They agreed and said when the 2004 Fifth Ed of BB was published they would include them. When the new BB came out it showed a S18a and S18b. I called them and basically they said sorry, just noted my patches incorrectly."
Randall holden writes about the MVE
"Any variations resulting from the manufacturing process belongs in the MVE category. If the difference in patches involves a color change, then this becomes an new issue (either an a/b variety or a new number)."
David Oertle provided the S17 set and Ed Dworak provided the 2S18 set. You may note that the thick Sanhican/WWW in the S17 set are a little darker in color compared to the other patches. I believe this is a scanner variation.