The JULIAN calendar was changed by Julius Ceasar in 709 AUC, that is 45 BC (hence its name).

[link to en.wikipedia.org (secure)]

It means that it was used in Christ's time AND location (Roman Empire) since the now universal calendar, the Gregorian calendar decreed to start on OCT 15 1582 AD, and adopted by all the nations since early 20th century, came far later.

I don't want nor need to use any other calendar since what matters is 1) the duration (not submitted to calendars) of the 7 churches fractal period (1986 years) and 2) when it falls in our time (need of a common time reference) from the perspective of Christ's past ministry (Christ's ascension year = 33 AD), provided that the fraction of year beyond the 1986 years in the 7 fractal periods' computing (half of the preceding period for each of them, starting with 1,001 years for the Day of God) are included in the remaining months of the year 33 AD beyond Christ's ascension day (to get a round year). The 13 days gap doesn't change a thing in terms of calculation (13 days included in the fraction).

So, the choice between the Gregorian calendar and the Julian calendar is not mine but those of the ET intel which clearly (now) add 13 days to DEC 31 2019 as mentioned in the OP several times, in several ways. That's why these ET intel are cryptic for many, many conditions must be fulfilled, even if APPARENTLY contradicting. This 13 days gap between the two calendars explains now these apparent contradictions.