I would somewhat agree with friedsquid. Allowing exception may look like inconsistencies within the grading firm and may reflect poorly on the TPG service, and trust may be compromised.
The Charlton guide does note that there are “Missing Circle” varieties out in the market, and they are non-errors and within the BofC tolerances.
I would 1st ask what are your parameters right now to determine if a note is perfectly centered or not? If you are using the missing circle to determine the centering of the note, then I would suggest that this may be the wrong approach. If you have graded an older $10 BABNC journey or a newer $10 note with the same amount of boarder on the left-side & right-side, as an UNC 65(+), then have you not already set a precedence as to what is and what is not acceptable for the UNC 65(+) grade?
I would agree that there should be a notation on the note being of the “missing circle” variety, as this is recognized by Charlton.
Just a thought, have you seen any other missing circle notes graded by other TPG sources, and if so what have they done?
If may be that a perfect “missing circle” note may be just like a true error note, sometimes perfection is slight less then.
FYI, I think it is great that you are doing your research.
Only my Opinion
Cheers