My M3 (S65) drains about 9.25qts from the sump. But has almost 2 quarts tied up in the oil cooler and lines.
And hilariously, my accord also hides about a quart somewhere. 4.4qts with filter change and something like 5.5qts at “engine overhaul” per the factory shop manual.
I have a plan one today to pull a sample of the old oil, fill with new oil, and pull another sample after running it for like 5 minutes, and send off to Horizon to check the viscosity drop just from the remaining old oil being mixed in. Because I have no life and nothing more fun to be doing.