The spreadsheet includes closed cases (approvals, denials and withdrawals), while most of the daily scans on VJ includes touched cases (including RFEs, RFERs, etc.).
The spreadsheet is therefore a better prediction of a decrease in overall backlog. The problem is that it also includes backlog reductions that are located behind most of our cases (i.e. denials for Jan'23 filers). The estimated wait time is a great sheet for everybody who's interested in seeing how many cases (cases received, RFEs, etc.) are still "open" in front of them. I have seen a lot of people trying to get as close as possible to actively tracking the entirety of the USCIS backlog and this spreadsheet definitely comes closest. As this is a December forum, I do not think it makes much sense for you guys as you have users doing great charts to track that specific month.
In case of any further questions, you can write the editors themselves:
contact: Telegram and Reddit @Obllak (Nikä Obllak), e-mail: nika.sumer@gmail.com