Do you mean we can retroactively calculate all the previous R values? That would be awesome then.
But as for recording the R values in revlog, I agree it’s weird to record something that can become obsolete. But that felt like the only option, besides Anki records difficulty anyway which is unhelpful and can be confusing even (people get confused when the D value suddenly change after a optimisation).
The goal is to evaluate individual performance rather. This is also useful if you’re comparing different hours of the day: