The Golden Bull of 1356

As anyone reading this can tell, sometimes I have extreme theories, but I am also very open to changing my mind if they are incorrect.

The Golden Bull was issued by Holy Roman Emperor Charles IV in 1356.  It was an important document about the constitutional structure of the Holy Roman Empire and we have multiple copies of it in Latin. Source in Latin.  Source in English.

Here is the part that includes the date (in Latin):
statuimus et duximus sacciendas sub anno Domini millesimo trecentestimo quinquagesimo sexto, indictione nona, quarto idus Januarii, regnorum nostrorum anno decimo, imperii vero primo

Google can't translate this but a very literal translation starting with "sub" is:
in the year of our Lord one thousand three hundred fifty six, in the ninth indiction, four before the ides of January, in the 10th year of our reign as king, the first as emperor.

The ides of January are on January 13, and I guess they use inclusive numbering, so 4 days before is January 10.  To get the proleptic Gregorian date, add a year (because the new year was on March 25 and this was before that), and add 10 days.  So it would be January 20, 1357 new style.  I think.

Anyways, the use of Anno Domini goes back further than I thought.  I still think that it was adopted at some point.