BeyondET,
The Sabbath that the Messiah honored was the Sabbath that his fellow countrymen used. They had honored it for centuries. If He had been honoring it on the incorrect day, then He would have been in violation of the Commandment and therefore not sinless.
So assuming that the Messiah knew which day of the week the Sabbath was on, we can know what day it is today. Although the calendar in use, a Roman calendar, has been changed, that change did not break the weekly cycle. Prior to the change, it was called the Julian calendar because it originated at the time of Julius Caesar, 45 B.C. - several decades before the birth of the Messiah. The one change was ordered by Pope Gregory, and since then it has been called the Gregorian calendar. However, as mentioned above, the change did not alter the weekly cycle. The "Catholic Encyclopedia", Vol. 9, p. 251, under the article "Lilius" says, regarding this change, that "every imaginable proposition was made, only one idea was never mentioned, viz, the abandonment of the seven-day week". Vol. 3, p. 740, under the article "Chronology", the same reference, says that "It is to be noted that in the Christian period, the order of days in the week has never been interrupted". So it would seem that the weekly cycle of the calendar that has been in effect since 45 B.C. has never had any alteration from the time of the Messiah until now. The Saturday of today is the same seventh day of the week as it was in the Messiah's time. One could, therefore, be pretty sure that they would be keeping the same Sabbath day that the Messiah kept, setting an example - the same day He said He was Lord of.
"The week of seven days has been in use ever since the days of the Mosaic dispensation, and we have no reason for supposing that any irregularities have existed in the succession of weeks and their days from that time to the present." --Dr. W.W. Campbell, Statement. [Dr. Campbell was Director of Lick Observatory, Mt. Hamilton, California.]
"As far as I know, in the various changes of the Calendar there has been no change in the seven day rota of the week, which has come down from very early times." --F.W. Dyson, Personal letter, dated March 4, 1932. [Dr. Dyson was Astronomer Royal, Royal Observatory, Greenwich, London.]
"I can only state that in connection with the proposed simplification of the calendar, we have had occasion to investigate the results of the works of specialists in chronology and we have never found one of them that has ever had the slightest doubt the continuity of the weekly cycle since long before the Christian era. So there has been no change in our calendar in past centuries that has affected in any way the cycle of the week." --James robertson, personal letter, dated March 12, 1932. [Dr. robertson was Director of the American Ephemeris, Navy Department, U.S. Naval Observatory, Washington, D.C.]
"In spite of all of our dickerings with the calendar, it is patent that the human race never lost the septenary [seven-day] sequence of week days and that the Sabbath of these latter times comes down to us from Adam, through the ages, without a single lapse." --Dr. Totten, Statement. [Dr. Totten of New Haven, Connecticut, was Professor of Astronomy at Yale University when this statement was made.]
The "Catholic Encyclopedia", Vol. 3, p. 740, article "Chronology" says: "It is to be noted that in the Christian period, the order of days in the week has never been interrupted."
If you have documentation that shows that the seven day cycle has been interrupted at some point between the first century and now I would very much like to see it.