Board Thread:General Discussion/@comment-28211557-20160310122940/@comment-86484-20161213113608

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 may be able to tell other things too.