Buried deep in the Electronic Reading Room, where USCIS probably hoped no one would ever find them, are two Freedom of Information Act files that individually record every I-526 and I-829 receipt and adjudication from October to December 2018 (FY2019 Q1).
Being diligent, I discovered the files, and immediately converted them to Excel and got to work with pivot tables. This data allows fact-based answers, at least for one quarter, to questions generally subject to rumor and speculation.