I sort by headstamp and year for target loads and weigh long range loads. But also use mixed brass of an unknown number of reloads and label them plinking loads for my son, his squeeze, and myself to blast away at whatever.
Re: headspace differences, obviously you should completely full length resize all brass to be used in the AR. The sizing will set the shoulder and thus the headspace. therefore all brass resized with the same die setting should have an identical shoulder location.
Oh yea, sorting is a pain. I use a magnifying glass to help.