Seems like there could easily be a day or two shift such that today's Sunday doesn't perfectly align (EXACTLY some large multiple of 7 day weeks ago) with the Sunday of ancient history.
Ah. Well, I am not a good person to ask about that. I never pay attention to those angles. I don’t believe the days have to perfectly align.
It isn’t magic that happens on one particular day over the other, it is a deep understanding of God’s ways and plans for us.
I am really only interested in what the Sabbath means and why.
Understanding that has been a huge blessing to me.
I do hope you find your answer.