Dear Instructors,

Years can be reduced to their kabbalistic number, as in, for example, 2021 = 5.
Considering that the there are other calendars which go further back than our Western one, on what grounds can we justify doing the kabbalistical addition?
After all, if there are different calendars, our kabbalistic number would show a relative result in relation to the year other calendars show that we are in.

Thank you!