i've seen people use BP (before present) where "present" is 1 jan 1950 (caused by radiocarbon dating shenanigans), if you're historian-adjacent, you might have not heard of this, but it's common in geology; at least that's what i thought until i came upon a paper (about pastoralism in neolithic northern africa) that was just using BP time like it was nothing, including dates like 1200 BP which i just cannot grasp and have to do mental math (so 0 BP is 1950 CE by definition, and seeing that BP is just distance from 1950 CE, then 1950 BP is 0 CE so 1200 BP is 1950 - 1200 = 750 CE)