Answer: It is Yahuwah who has preserved His Scriptures.  Scriptures states that when the Israelites were unfaithful to Yahuwah, as a punishment He caused them to forget His true New Moons, Feasts, and Sabbath.

“I will also cause all her mirth to cease, her feast days, Her New Moons, Her Sabbaths -- All her appointed feasts,” says Yahuwah. Hosea 2:11

Remember, 490 years of probation was given to the Israelites until Yahushua came on the scene.  Then they totally flunked the test of recognizing Yahushua as the promised Messiah, and fulfilled prophecy by putting Him on the cross.  After the stoning of Stephen, the gospel then went to the Gentiles and finally in A.D. 70 Jerusalem was destroyed and taken captive, thus the Israelites succumbed to Rome, her laws and her calendar.  The calendar at that time was the Julian calendar, which had only recently been created in the year 45 B.C.  As long as Israel had been faithful to Yahuwah, she had remained a sovereign nation. In those early days the week was an eight-day successive chain of weeks that rotated through the months.  This is the earliest recorded period of an existence of successive cycles of weeks.

In the mid-1st century B.C. Julius Cæsar invited Sosigenes, an Alexandrian astronomer, to advise him about the reform of the calendar, and Sosigenes decided that the only practical step was to abandon the lunar calendar altogether. Months must be arranged on a seasonal basis, and a tropical (solar) year used, as in the Egyptian calendar. “The Julian Calendar”, Encyclopedia Britannica.

The Israelites as a organized unit did not recognize their own Creator and rejected Him.  Yet you believe that after all that, this same renegade bunch would still carefully protect the true Sabbath, when they couldn’t and wouldn’t protect the true Savior?