Interesting that there seem to be a large number of scholars who would accept either 4 AD or 8 AD was the first AD leap year. But less clear what such a year wo

Interesting that there seem to be a large number of scholars who would accept either 4 AD or 8 AD was the first AD leap year. But less clear what such a year would have been called by Romans at the time. I'm assuming it wasn't common to include full dates (including the year #) on written documents at the time, otherwise surely we'd know pretty much exactly. I gather AD-based year numbering wasn't actually introduced until ~525 AD (but before that a number of systems had been in use).