Board Thread:General Discussion/@comment-28211557-20160310122940/@comment-30501299-20161214045741

Gabi wrote: There's no way to tell whether or not they use the same system as the humans. They have imitated a lot of things humans do, but they may or may not have copied that. In any case, if you read my post again, you will realize that I never made that assumption. I used the dates as shown in the game. Whether or not those dates match ours is another story and is not what I was discussing (since there is no way to know).

And Sans can tell more than just how many times you have died. He can tell how many times you have killed him, how much EXP and LV you have, whether you have accepted his offer to spare you before, and whether or not you've heard his speech before. So it's not much of a stretch to assume he's be able to tell other things too. I think the x dating system makes more sense as they clearly imerge in around this tme, when DVDs are still used, polution hasn't blocked out the sun and when Star Wars jokes like "Loox Eyewalker" when Chara provides the check data are still relevent. He probably can tell more though given the way he sometimes gets the numbers wrong after several deaths and can't keep track after 11 I would assume it is mostly reading your expression and body language like cringing at his spare, a smug look if you killed him or anger after som many deaths adding up with you maybe even counting in anger.