Oh, this poll is interesting and I don't honestly know how to answer it. Are we talking rifle, for plinking, for blammo? Are we talking pistol for semi auto, for revolver?
I have different levels of headstamp sorting consistency ranges for the different cartridges I load.
For rifle I mostly sort by headstamp. Revolver calibers I sort by headstamp as the brass thickness does vary and I do load cast. For 45 ACP I ended up sorting by headstamps when I got a large batch that included military cases from the 40s and 50s. For all other semis I load whatever mixed bag of cases are around. And of course to sort out small primer cases.
And, based on Arkansas Paul's estimation -- I may need professional psychiatric help! 'Cause in 9MM and in 380, and even 40 S&W, I've been known to just throw all the cases together, including brass and nickel.
So, how do I answer the poll?
For 9MM, 380, 40 and other pistol rounds -- add that 100th case and carry on.
For rifle - load the 99. Then start another headstamp batch for the other 101.