If I understood you question correctly, I would definitely answer it with a no. There are too numerous historical events throughout the history of our current western calendrical system which can be pinned down to a specific day, AND which were recorded by independent sources, which makes it very unlikely they got it all wrong. Think alone of predictable events like a solar eclipse. We can calculate the exact date at which they have taken place in the past and compare this to multiple independent ancient records.

Linguist here. Today is Wednesday because we all agree that it's Wednesday. Today is February 19th, 2015 because we all agree that it is February 19th, 2015. A legislative body could pass a law requiring its nation to now abide by an 8-day week. The people in that nation would then be agreed, legally, that their week is 8 days long. Obviously that scenario won't come to pass, but time is an illusion. There is no inherent "Wednesday-ness" in today. You cannot grind today down into the finest powder and show someone a fleck of February or a speck of the 19th or a modicum of 2015. We have agreed on terms and definitions to suit our needs, nothing more, nothing less.