I think if you do some research you will indeed find that days have been added and subtracted from the "Official" calendars over the centuries. What I also have found is that the cycle of days has never been broken. For instance, when The British Calendar Act of 1751 added eleven days, the day after Wednesday the second became Thursday the fourteenth etc.,etc. The seven day cycle remained the same.
Mark was not an eyewitness to the events. Mark only wrote down what he heard Peter say.....sometimes, not in the exact sequence. Papias was a companion of Polycarp and also heard the Apostle John speak. (See section VI) He relates these things to us in his "Exposition of the Oracles of The lord". Papias tells us that Mark was careful not to omit anything but sometimes his writings were not in exact order.
Consequently we read in Mark 16:2, [Very early on the first day of the week, just after sunrise, they were on their way to the tomb and they asked each other, "Who will roll the stone away from the entrance of the tomb?"] Mark has just made a three day leap in time to Sunday morning from Thursday night between verse 1 and 2.
These are not the same women! In Matthew 28:1 the women arrive at the tomb "Late on the Sabbath", about sundown. And in verse 8 they hurry away to tell the disciples. In Luke 24 :9 they again "tell the disciples" after finding the tomb open and empty. Also John 20:2 shows Mary the Magdalene running to "tell the disciples". All these events have taken place shortly after sunset of the Sabbath.
Only in Mark 16:2 do we find "they" were on "their" way to the tomb on the first day of the week after "sunrise". Verse 8 tells us this group of women, after being told to go and tell the disciples....say nothing to anyone, because they were afraid. When you realize that Mark is not speaking of the same group of women and makes a three day leap in time between verse 1 and 2, then Mark's narrative begins to harmonize with Matthew, Luke and John.