No, you need a lot more complexity if you really wanted to represent it semantically. The assumption that people in the past used calendars with sequentially numbered years you just need to offset, is simply wrong.

You have things like "in the Xth year of the reign of King Y", where we can easily relate multiple entries with different values for X, but don't actually know which CE years they correspond to. Even weirder is the Roman habit of recording "the year of the consulship of X and Y", which doesn't even allow you to relate any two different years at all without a reference table (which we don't have completely). And no, "years from the foundong of the city" wasn't a thing.

I actually looked at supporting dates like this, but if you go through the Met's open dataset (https://github.com/metmuseum/openaccess) that kind of "alternative calendar with no reference to the BCE/CE dates" is basically nonexistent.

There are references to the Islamic and Japanese calendar systems, but always next to the CE equivalent.

Data entry is fortunately being done by modern people, so the translation to CE/BCE is usually baked in, and all you need to support is every possible way somebody could say "the early half of" and "5th millenium B.C. to mid 1914"

Mostly true, but not absolutely:

https://en.wikipedia.org/wiki/Varronian_chronology

> The Varronian chronology was adopted by the Roman state during the first century BC and gave rise to the traditional years ab urbe condita ("from the founding of the city"); most especially, those dates were used in monumental Augustan-era inscriptions, the fasti Capitolini and the fasti Triumphales.[40]