Out of curiosity, I decided to try sorting MSE questions by age from back to front, and I noticed something odd: while the second through $48^\text{th}$ questions are all from July 20, 2010, there is a single earlier post, from March 27, 2010. It has a few comments dated March of 2010, as well.
Furthermore, the URL of this post is weird. Every MSE question or answer is assigned a unique positive integer identifier, counting up one at a time. https://math.stackexchange.com/questions/1
takes us to the first of these July 20 questions, but the sole earlier post has a URL of https://math.stackexchange.com/questions/106814
, and its answer a URL of https://math.stackexchange.com/questions/106815/
. Compare to https://math.stackexchange.com/questions/106813
, which dates to 2012-02-07 21:37, and https://math.stackexchange.com/questions/106816
, which dates to 2012-02-07 21:46. (I looked at several questions from that evening and wasn't able to find any "ghost" questions or answers in the interval between 21:37 and 21:46.)
In fact, if one looks at the profile of the user who posted this first question, as well as that of the only contemporary commenter whose account remains, neither one's account age is compatible with having used the site in March of 2010, as they both appear to have made their accounts later that fall. In fact, the apparent earliest user of MSE whose account is viewable seems to have created their account on July 20, 2010.
I checked MathOverflow and StackOverflow, and a similar phenomenon does not occur; the first question has some very low-indexed URL as expected, and was written by a sufficiently old user.
Doing some archaeology on the Internet Archive, I can find a single snapshot from 2009 (!) which displays a single question by Brian R. Bondry. Current MSE pages show the index-1 question as this one, and the user as being #53. (Frustratingly, no 2010 snapshots appear to have been taken after January of that year.)
What's going on here? Are there any MSE veterans who can shed light on these weird relics of the earliest days of the site? I'm very confused.