From the original release of Sentinels of the Multiverse in 2011, one of the noteworthy features of the game was the fact that the Hero and Villain cards all had flavortext quotes attributed to specific issues of the fictional Sentinel Comics the characters and story beats were purported to be from, lending a sense of verisimilitude and history to the characters created for the game. Christopher and Adam invented broad story beats for their characters and had a good sense of what sorts of events happened along the way in their created universe.
Unfortunately, what they hadn't done was think through all of the issue numbers they were assigning along the way. Especially in the first edition of SotM, the issue numbers chosen were more or less arbitrary.
As The Letters Page podcast got started, they began letting the fans in on the stories of Sentinel Comics as well as the timing of events in what we've come to call the Metaverse - the universe where Sentinel Comics is a publisher and where these comics all actually exist. It more or less maps to the real world, just with the addition of Sentinel Comics as a major comics publisher throughout the years. Things like the "Golden Age" of comics and the Comics Code Authority still existed, as did trends in comics publishing like the 1980s being a bit darker and grittier than the Silver Age of the 1960s. If you can think of something in our world related to comic books, there's likely a similar thing happening at that time in the Metaverse.
However, as the podcast continued and they were approaching the point of the OblivAeon expansion's release and the episode about Sky-Scraper they came to the conclusion that at least some of the numbering was off. For Sky-Scraper to work as a character subverting audience expectations of Thorathians, the alien invaders and their leader would need to have been established much earlier than they had previously stated in game materials. Additionally, with the Sentinel Comics RPG on the horizon they felt it was time to actually work through the publication timeline.
Sometime in late 2017 or early 2018 Christopher and Adam began a long process of sorting out the publication history of their entire fictional comics company. From what we've been told, this involved placing sticky notes along the walls of the Greater Than Games offices showing where individual comics aligned with one another and moving/replacing them where appropriate to make sure everything fit. Having finished that, they moved on to recording that in a spreadsheet where every issue number is laid out for the entire 80 or so year history of Sentinel Comics. Not every issue has known details, obviously, but all major events as they know them are recorded as well as allowing them to easily find appropriate spots to fill in during Creative Process and Writer's Room episodes when they invent additional detail.
However, this means that any citation to a specific issue or event in the history of Sentinel Comics that was given prior to 2018 is no longer necessarily true. The details given about character and story are likely still applicable, but when they happen may have been adjusted in the meantime. This essentially means that no materials from SotM, Sentinel Tactics, or the first year of the podcast can be relied upon to give accurate issue numbers or dates. Many may still be correct, since the card attributions were what were used to try to line things up, but we can't be certain based on that evidence alone. A knock on effect is that many pieces of art do not have an art style befitting the issue in question. As a notable example, the version of Freedom Four Annual #1 that Christopher and Adam created shortly after the game was released was revealed to have been created in 1957. This means that the art style is entirely too modern and even specific setting details like Tachyon being married to Dana Bertrand are decades out of place. Even things as recent as the ARG Event and the OblivAeon expansion content were too far along in the production process to adjust.
As such, this summary is mainly here to act as a disclaimer: Anything related to the timeline of publication of Sentinel Comics, including pieces of art like comic covers, that were talked about or produced prior to 2018 cannot be assumed to be canonical.
The Sentinels of the Multiverse: Definitive Edition, which had its core set Kickstarted in April 2021, seeks to remedy this issue. All card flavortext attributions and the depicted comic panel in the materials for this new edition will have correct issue numbers, dates, and era-appropriate art.