Converting between Hebrew and Gregorian dates for very early years is mathematically possible (and is supported by our Hebrew Date Converter), but the results should be treated as approximations rather than historically precise dates.
The Hebrew calendar evolved into a fixed, calculation-based system beginning in the 4th century CE, traditionally associated with reforms attributed to Rabbi Hillel. This shift replaced earlier dependence on eyewitness moon sightings and centralized rulings on leap years with a predictable mathematical framework. The detailed rules were recorded in writing over the following centuries and were later systematized by Maimonides in the 12th century, by which point the calendar had become uniform across Jewish communities by the medieval era.[1]
Before the calendar rules were fully standardized in the early medieval period, both the Hebrew and civil calendars were influenced by local practice, observational methods, and later retroactive calculations. As a result, modern algorithms can project dates backward consistently, but they may not reflect how dates were actually observed or recorded at the time.
Any results for year 1752 CE and earlier published on Hebcal.com will be inaccurate. Hebcal does not take into account a correction of ten days that was introduced by Pope Gregory XIII known as the Gregorian Reformation.
Encyclopædia Britannica has an excellent introduction to the Jewish calendar. Another well written treatment of the Jewish calendar can be found in Understanding the Jewish Calendar by Rabbi Nathan Bushwick.