We know from history that the Julian calendar was off by four years. Could you elaborate on what error you mean? That the Romans didn't correctly apply the leap years, or that a 4-year error accumulated over time, or that a leap year is inserted every 4 years, other?...a link to anything is always helpful.
If we are using 6BC then 458BC for the command would put the death of Jesus at what? 26AD? [458 -1+26 =483]
Or If we are using 2BC then 454BC would be the command. [454-1+30=483] with the death of Jesus at 30 AD.
The question is which date is written in stone and what did the Gregorian Calendar correct? I don't have any links but I will look for some. I have been looking for some way to tie down those decree dates for awhile, but I am not sure that it is possible.