Release dates are a special project of mine that I have been researching/compiling for more than a decade. My data comes from many sources. Many of these sources can only provide information about a particular time period.

For books from 1935-the early 1960s house ads are my primary source of data. Many comics from the early 1940s and 1960s had release dates for individual issues. While I've found release dates for only a small percentage of these comics, it is possible to detect patterns in the releases. These patterns can relate to the order within a month in which titles are released (ex. Flash Comics went onsale about 5-7 days before All-American Comics). The patterns also show that an individual title was generally released around the same date each month (ex. Flash Comics was released around the 15th of the month each month). The patterns can also determine what days of the week books were usually released (generally Tue & Thurs, but sometimes Wed/Fri for Quarterly books of the 1940s). Using these patterns based on the "real" release dates found in the house ads I've been able to put together remarkably accurate release dates for books that were not given in house ads. I do continually search out new data points in old house ads. The accuracy of my estimates is quite good based on newly acquired house ads dates. Its about generally within 5 days for 1940s books, 2 days for 1960s books, and 10 days for 1950s books. The 1950s were rather difficult because few 1950s house ads listed dates and many titles changed frequency (ex. going from bi-monthly to 8 times a year). My database reflects whether or not the release date listed is a "confirmed date" (one given in a house ad) or an "estimated date" (one I've estimated). The confirmed dates say: "On Sale : xx/xx/xx" while the estimated dates use the verbage "Aprox. On Sale: xx/xx/xx". Periodically I do revise my estimates as new data points are found.

For books after 1960, I have much more reliable data. DC began printing "Direct Currents" in their books in the mid-60s. These listed release dates for most titles. From about 1976-1982 release dates can be found in the "Daily Planet" sections in many comics. From 1984-1990, DC published giveaway pamphlets called "DC Releases" and then "Direct Currents" which contained release dates for everything. For 1990-up I use the release date from Diamond Previews. (Yes, I have every issue of Previews from 1990-present). With the modern stuff, it is fairly common for books to ship late by a week or two. I continue to use the original solicitation date rather than adjusting for lateness.

I have never known of anyone that has even attempted to compile release dates on this scale. I'm sure the publishers themselves might have some records of this data, but there is no telling how complete it is, especially for older stuff. I consider myself to be an expert (if not THE expert) on the subject, especially for Golden Age stuff. However, my knowledge is limited to DC only. I'm sure it would not be hard (though it probably would be time consuming) to compile data for Marvel from at least 1980-up. They may even have dates in the Bullpen Bulletins from earlier books. I personally have no interest in Marvel or any other publishers. If you want the data, I would recommend compiling it yourself. It will take time and you will probably be missing stuff, but there's nothing like doing it yourself.

UPDATE 2013: This article was written prior to the creation of my Marvel website. Beginning in 2010 I did research Marvel data and the results can be found in my database.

For additional info regarding release dates, here's a link to my article: Secrets to DC Cover Dates