It turns out that having the preamp powered down for an hour, hour-and-a-half *isn't* long enough to get it back to whatever initial condition that causes the white noise. (I put the preamp back into my system and listened. When powered down for six hours, I got the white noise; when powered down for an hour, I did *not* get the white noise.)
So the OA and Breg measurements are probably OK (they were both done on a system that had been powered down for more than 12 hours.)
The OB and IA measurements were done on a system that had only been powered down for about an hour, so I'll redo those. I also got a new 12BH7, so having that option, along with the option of re-doing solder joints, should keep me busy, since I only like to make one change at a time hahaha.