Lobuttomize said:
Seems like an inconsistent way to handle it
Not really. All of the other 'related' pools and tags are also handled in a similar manner. The Current Events pool itself has a list of some of them:
Current Events pool says:
pool #1318 - In Memoriam
pool #1823 - Wow That Was Fast
pool #3097 - Pray for Japan
pool #16384 - Virtual Graduation Commemoration
satire
coronavirus pandemic
pool #15915 - Arknights - Myths & Truths about COVID-19 (AcrylicStroke)
pixiv tag: 時事ネタ
Coronavirus pandemic being the most prominent example, as it is an ongoing event (that is not going to go away anytime soon, if at all). Only notable 'updates' (like Japan instituting new quarantine policies or mask recommendations) go into the Current Events pool, and only while said news remain current.
The general idea is that "Current Events" is used for "hot news". Once multiple posts depicts the same event, it is no longer "hot".
This is also related to how non-series pools are handled in general. Posts should be 'notable' enough (stands out among other posts) to warrant their inclusion into a pool. Sometimes a post has elements that may seem to justify its inclusion into two more more pools. But careful consideration will oftentimes show that it is only notable enough to "stand out" in one (or two, or three, but not all), while being drowned out by other "better examples" in other pools. Because the criteria for "standing out" differs from pool to pool. And for Current Events it is currency, i.e. the quality of being "hot news".
Meanwhile, for Virtual Graduation Commemoration (and In Memoriam), the criteria for "standing out" is commemoration, i.e. the post is dedicated as tribute or commemoration to a specific person or entity. So in this case, any drawing that alludes to a V-Tuber graduating (either explicitly or implicitly enough to justify) is sufficient to qualify.
So, first few posts for a specific V-Tuber graduating, okay, it's notable, it's hot news, so, into Current Events it goes. The twentieth or so? No, we already all know by that point. It's old news. Yes... technically it only happened just recently, but it's still old news... mm'kay?