There’s some fun to be had in hunting up references to and citing instances where volumes from Migne’s Patrologia latina exist in different versions.
The folks at SBL Press have kindly resolved the mystery. Most significantly, SBL Press notes,
According to the Patrologia Latina Database … , PL’s printing history can be divided into two distinct periods. Jacques-Paul Migne initially published the 217 volumes of PL over a twelve-year period, 1844–1855. Migne reprinted volumes as needed for another decade, then sold the rights to the Paris publisher Garnier. Unfortunately, in February 1868 a fire destroyed Migne’s presses and printing plates, which meant that Garnier, which had begun reprinting some PL volumes in 1865, was the only source for future reprints—all of which were produced on plates other than Migne’s originals. These plates differed substantially in some cases and are considered in general “inferior in a number of respects to Migne’s own first editions.”
What does this mean for researchers today who need to cite PL? SBL Press recommends that authors always check a PL volume title page to ensure that the printing is dated 1865 or earlier. If the publication or printing date is 1868 or later, we encourage authors to find an earlier printing of PL to cite. (emphasis added)
For additional discussion, suggestions about finding earlier printings, and recommendations for how to cite the later batch of printings if need be, see the SBL Handbook of Style blog.