I'm not sure I understood well the question... if you're asking about the seven-day-week cycle, we can be pretty sure that it has gone on unbroken since the first centuries of Christian Era.

The Church has always been very keen to preserve the week cycle, because of the holiness of Sunday (and Saturday, if we consider the Jewish antecedents) and the importance of determining the date of Easter.

Of course some individual, or traveller, or farmer in an isolated country, or someone else could hav lost track of the days and skipped a Tuesday or two, but the Church as institution assured the continuity of the seven-day-cycle at least since the 3rd century AD.

Even in the calendar reforms the cycle was not broken: adopting the Gregorian calendar the Catholic world went from Thursday, 4 October 1582 to Friday, 15 October 1582 (which was 5 October for the countries still using the Julian Calendar, but still a Friday).

We can align various calendars from the dates of eclipses and other astrononomical phenomena, which some cultures kept good records of a long way back (for instance the Babylonians and Chinese). This means we can be pretty certain of particular dates in history, and - for instance - if someone felt that we should add or subtract fifty years from the "dark ages", this could be dismissed.

During the transition from the Julian to Gregorian calanders many days were dropped. However, this can vary since it took centuries for everyone to make the switch. So dating exact dates of events can be somewhat tricky. For instance, there was almost a 2 century lag between France making the change, and England making it, so events the countries both document, could have differing dates, depending on the calender used.

http://www.timeanddate.com/calendar/julian-gregorian-switch.html