HISTORIANS: We've decided to trim the past down to make things more manageable. Using BCE/CE, would you rather we lose the odd-numbered or even-numbered years?
This comic quotes a lengthy section of the Bloomington Daily Pantagraph's September 30, 1881 issue. The tragic event referenced throughout is the assassination of President James A. Garfield. Interestingly, the article is about how closely studied the incident will or will not be in the future. Garfield's assassination is rarely more than a quick note in a history class, leaving only the "dry and tedious" historians to comb through the details.
The writer also notes that vast quantities of accounts exist of the national grief and trauma caused by Garfield's murder, and wonders whether students in the future will bother to read those accounts to understand it, or simply let historians sum it up without conveying the vastness of the response. That fear at least did prove well-founded; most students are not aware of the fallout of the assassination, or indeed, of Garfield at all. Cueball and Megan are discomfited by the fact there exists a vast, untapped store of information that they have never read, about an event they know little to nothing about despite it apparently causing nationwide trauma. This leads to a larger point about the vastness of history, and the impossibility of learning all of it.
The article itself references other events that would have been in recent memory at the time of publication and draws some conclusions about which will be considered more important in the future.
For example, it cites the defeat of Roscoe Conkling as a serious event that would fade in importance when compared to Garfield's assassination. Conkling was a senator in Garfield's party who resigned in protest of Garfield's policies assuming that he would easily win re-election by the state legislature--but then failed to achieve re-election due to party factions and political infighting.
Interestingly a comparison of Google search frequency for the years 2004-2018 shows that Garfield is indeed searched for many times more often than Conkling. Conkling's failure to be re-elected by the New York state legislature, which seemed so vitally important at the time, is summarized by a brief two sentences near the bottom of Conkling's Wikipedia article and not even mentioned in the biography's summary. So the writer does appear to be correct that Conkling's re-election defeat was an episode that was of high importance as a current event that in the future was to become not much more than an obscure footnote.
The writer speculates that there may not be any event in American history that matches the level of grief caused by Garfield's assassination, not even that of Lincoln. Here the writer is further off the mark, because in current historical memory, the Lincoln assassination is still a towering, defining event, whereas Garfield's is, comparatively speaking, a footnote.
The bolded sections of the text emphasize some of the main points of the article for the modern reader and may also be another way Munroe makes the point that future readers are unlikely to have the patience to read lengthy, detailed explanations of past events. If they have time to pay attention at all, future readers will want the essence boiled down to a few major highlights.
The title text indicates that there is more information about the past than can be researched by the manpower of available historians at this time. For whatever reason, be it lack of funding to carry out research or lack of interested people becoming historians, the facetious solution is to just ignore events of either even or odd numbered years. This would essentially halve the amount of data to go through and the amount of time to go through it, but it would be at the detriment of our understanding of all of the context of said events. As an example World War 2 started and ended on odd years, but some of the most tide-turning battles (Fall of France, most of Stalingrad, D-Day) happened on even years.
Although this format with small panels above and below a larger one has been seen before, there could be an extra joke this time, if it is seen as if there were originally five panels to the comic, but the second and fourth (the even ones) were removed.