have you ever heard that astrological signs are
- there's some accounting-error,
since the zodiac signs were established?
and that they work much better if you shift your birthday forward for correction.

There's also a theory that several years were added surreptitiously
to the calendar-system to inflate the reputation of the roman empire.

There's also the surprisingly-serious problem of year-0 AD:
Do we go from Dec 31st 1BC to 1AD, or 0 AD?
Amazingly, like "bi-weekly", it depends on who you ask.

there was also the switch to the gregorian calendar,
(very) recently.
which added between 11 and 13 days
(depending on when the country made the switch)
..and by the time the whole world was on the gregorian calendar, we were
in WWI.
The drift of the Julian calendar (11 minutes), from when it was proposed (46 BC) to today (2018) -
is nearly a full month's discrepancy

Personally, I'm trying to record
details of every day since 2009, in my life.
- using bank-records, sms-transcripts, search-history -
it's nearly impossible.
and I'm a software developer
that wrote a big timezone library.

our seconds since 1970:
is this true?
(Dennis Ritche, creator of Unix time, on or around 1970)
how far back do we have to go to find the first
global timeline error?
actual confident timeline begin?

Unix time is lovely. it is a good, simple, non-astronomical calendar system,
but it is pegged to the gregorian calendar, on Jan 1 1970,
whichever that point is.
if we define our actual calendar as before/after Unix time, we may find Columbus landed on year 1621 or '349 Before-Unix' - we may find christ was born in 25AD or '1945 BU'.
Like Unix time, astronomical time has been ticking along properly all along.
You can imagine immediate implications for our flawed human-recorded dateline in astronomy.
Spielberg re-mastered the night sky in reproductions of the Titanic, to be more astronomically-accurate.
I have many doubts that his reproduction is correct.
Not only were passengers, and clocks on the ship, between timezones global time-zones weren't even implemented yet.
The titanic sank in UTC-3, but I doubt very much that it was observed on-board.
(Sanford Fleming, my guy)
We live in an mostly-unambiguous time system now, but we must admit that this did not develop until very, very recently.
The correct time, or even the correct day, ought to be doubted even into the 20th century.
The correct decade, ought to be in question for anything further back.