For a long time, the Callbook was published 4 times a year, in the following order: Spring, Summer, Fall, Winter. You'd think the Winter issue would be first, but it's actually last.
Jim -
Yes, that was true "for a long time", from 1926 to 1977. For example, Volume 50 was 1972, and numbers 1 through 4 were Spring through Winter, respectively. But that changed at the end of 1977. V55N3 was Summer 1977, but the Winter 1977-78 issue was labeled V56N1. They actually skipped V55N4! They continued that way through V63N4 in Fall of 1985. V64N1 was Winter 85-86, but they moved to a single supplement in the summer, with V64N2 as the Summer 1986 supplement.
I think this was so they could start calling the Winter books by the succeeding year's number. Although the inside title page would say "Winter 1985-86", the cover would say "1986 Callbook." That would have looked suspicious if the 1986 Callbook was actually the fourth issue in the previous year's series. Earlier issues (pre-78) used the phrase "for use through 1977", for example, for the Winter 76-77 book.
In fact, you can see that on archive.org.
This section has the cover showing "1978 Callbook", but if you turn two pages in, you'll see it listed as Winter 1977-78 and V56N1.
Steve
P.S. It's interesting that this post is gaining recent traction, considering that I answered the OP's question over a month ago, that his first listing was in the Summer 1977 supplement (V55N2). How did I know it was the first listing? Because supplements at that time ONLY listed calls that were issued or changed since the last issue. So Summer 77 didn't include anything that would have been in Spring 77, or any earlier books.