A year zero does not exist in the Anno Domini (AD) calendar year system commonly used to number years in the Gregorian calendar (nor in its predecessor, the Julian calendar); in this system, the year 1 BC is followed directly by year AD 1.
THEREFORE: BC 1 and AD 1, both begin with the year already counted.
ONLY when BC1 and AD1 are over has 2 years elapsed.
BUT, on your chart #1, you make BC 1 & 2 and AD 1 & 2 add to 4 years, when actually only 2 have passed.
TO CORRECT this situation two year zero's must be added at the BC/AD changeover.
Furthermore, your year 20 BC is only 19 elapsed years and year 30 AD is only 29 elapsed years, total 48 years.
Soo, we establish the date of the crucifixion......what then?
Adam to Abraham; exactly 2000 years.
Abraham to Jesus, exactly 2000 years.
Jesus' Ascension to Return, now 1992 years and counting.
The Millennium reign of Jesus, exactly 1000 years.
Gods decreed time for mankind, exactly 7000 years.
Got any ideas what's next for us right now?