Although I usually completely shun the attitude of "good enough", there does come a point in time where an obsessive quest for perfection does have to be mitigated and ended with this advice: "It's good enough." After many hours of searching for the best method, I think you've now arrived at that point.
I do this, too. Many of us do. It's not just you.
Although it may be interesting to discover the variations in values -- something that I just really can't explain either -- it may not affect the end-product. That's when "good enough" kicks in.
It may require the knowledge of a video/broadcast engineer, the people that create this stuff, and not us end-users. If you ever do find the answer, please post it here for all to read.
You're also correct when it comes to bit depth. Although it looks good on paper, and becomes the bragging points for tech geeks and company marketing departments, it doesn't often have a lot of real-world meaning. I run into this with scanning, DSLR RAW images, video codecs, etc. --- there is a "good enough" with bit depth, too!