There are three "error" issues I can think of of the top of my head. The 271a (6c Garfield) and 272a (8c Sherman) both appear with USPS and USIR watermarks. Also, the $1 Prexi (832b) appears on the USIR double line watermarks.
Now... the rule for this is, a large enough % of either the lower leg of the "I" or the base of the "R" as a minimum must be visible to call it a USIR watermark. Interestingly, even in a block of say 4, if 2 of the stamps have U or S on them, those stamps are NOT considered to be watermarked 191. So if you get a block, with the intent of breaking it up into singles, ONLY those singles with discernable % of I or R on them will count. The others are considered 191 watermarked.
Some try to claim when only the leg of the P from USPS is visible that it's a USIR, so you have to very accurately measure to see if the leg is longer than where the base of the curve of the P would connect with the line. If it's past that, then you've got yourself a USIR watermark.
Comments
Actually, not the case.
There are three "error" issues I can think of of the top of my head.
The 271a (6c Garfield) and 272a (8c Sherman) both appear with USPS and USIR watermarks.
Also, the $1 Prexi (832b) appears on the USIR double line watermarks.
Now... the rule for this is, a large enough % of either the lower leg of the "I" or the base of the "R" as a minimum must be visible to call it a USIR watermark. Interestingly, even in a block of say 4, if 2 of the stamps have U or S on them, those stamps are NOT considered to be watermarked 191. So if you get a block, with the intent of breaking it up into singles, ONLY those singles with discernable % of I or R on them will count. The others are considered 191 watermarked.
Some try to claim when only the leg of the P from USPS is visible that it's a USIR, so you have to very accurately measure to see if the leg is longer than where the base of the curve of the P would connect with the line. If it's past that, then you've got yourself a USIR watermark.
You are correct.