<p>The "Winter" issues fall into three categories.
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(1) Books dated "Winter" published between 1939 and 1976. This was used only for books that were published quarterly (although some books, like <i>All-Star</i>, went back and forth between quarterly and non-quarterly). A full list of these "Winter" books is here:
[1] As I mentioned earlier, DC was inconsistent about what year to list in the indicia for a Winter issue; you can get that date from GDC's links, and then use the "cover gallery" link to see where this issue fits chronologically and determine what the actual year was.
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(2) Books dated "Winter" published in 1988. A huge number of books fall into this category, and they all use the same sequence: December 1988, Winter 1988, Holiday 1988, January 1989. A <i>partial</i> list is here
[2], but I believe GCD occasionally erred in its listings of these, simply repeating "December, December, December" for all three sequential issues. This is probably because, in some cases, DC didn't print the date on the cover of the issue (e.g, Doom Patrol #16-17 and Batman #427-428, which are Winter 1988 / Holiday 1988 issues according to the indicia but not the cover).
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(3) Books dated "Winter" published between 1990 and 2001. During this time, seasonal dates were used only for books that were published quarterly. I am 90% sure that during this era, the year was always the later year (in other words, "Winter 2001" means 12/21/2000 to 3/20/2001), although in some cases they actually specified both years (example:
[3]). A full list is here:
[4] Note, however, that GCD itself has errors in the year: if you look at the Batman Chronicles you'll see that GCD lists both #11 and #15 as "Winter 1998", when the latter should be "Winter 1999".
</p><p>DC never used "Winter" between 1977 and 1987 inclusive (proof:
[5]), nor between 2002 and the present (proof:
[6]).
</p><p>If you follow these links and then click on "Refine your search using the advanced search", you will see the fields I used to search for these, and can modify them accordingly. Be sure to select "Cover" in the "Type" box, or else you will get duplicate listings, one for each story, ad, and so forth in the comic.
</p><p>Anyway, I agree that, if the software supports it, this wiki should actually display "Winter", "Summer", "Holiday" instead of converting it to a month that did not actually appear on the cover. If we do so, we still have to decide whether to force consistency on the <i>years</i> of Winter issues.
</p><p>It's less important to display a "March-April" issue as "March-April"; many websites simply list such as "April" (GCD is one of the few websites that consistently records double-month dates). Using the second month doesn't cause any problems, although in the late 1960s it occasionally produces slightly strange results: for example, Batman #185 was "Oct-Nov 1966", #186 was "Nov 1966", #187 was "Dec-Jan 1966-67", #188 was "Dec 1966" -- but that was because Giant issues always got two months and regular issues one month, even if the results occasionally seemed to go back in time.
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