Scott #580? What Happened?

It appears that the catalogue is missing 580. Am I loopy or is this on purpose?
I have 579 perf 11x10 and a 581, then I have a space in my album that asks for a 2 cent G.W. perf 11.
My catalogue information doesn't have a 579a

You are correct ... there is no US Scott 580. (I don't know when it was rescinded, but it isn't in my 2008 catalog, so must have been earlier than that.)

There is no #580 in the 1925 nor 1940 catalogs, but for different reasons. In 1925, it looks like #580 was reserved for a 3c stamp in the set. Even though subsequent re-numberings made major set number shifts/changes for that catalog number range, it appears that #580 remained an extraneous number between sets, and remains unassigned to this day. Obviously, I don't have all the catalogs in between, so I am subject to correction/clarification.

I do not have the 1923/24 Scotts either, but I suspect the explanation is:

before the airmails were moved to the back of the book [and before the perf 11x10 varieties were recognized], C4-C5-C6 were 578-579-580. There is also a 'hole' at 520-521-522 where C1-C2-C3 were originally.

#580 is not in the 1928, 1929, 1931 or 1939 cat. either.

I had also wondered about that and checked into that possibility before I posted. The current C4-C6 were originally #589-591.