Is it possible that The Jewish people could lose track of The Passover?
How could such a thing happen?
Scripture makes it plain that not only is it possible for The Jewish people to lose track of the proper observance of The Passover that it has already happened before, and the circumstances of their past forsaking has been repeated in modern times.
When King Josiah instituted reforms the priests cleaning out The Temple found The Law, the first 5 books of The Bible.
And Hilkiah the high priest said unto Shaphan the scribe, I have found the book of the law in the house of the LORD. And Hilkiah gave the book to Shaphan, and he read it. And Shaphan the scribe came to the king, and brought the king word again, and said, Thy servants have gathered the money that was found in the house, and have delivered it into the hand of them that do the work, that have the oversight of the house of the LORD. And Shaphan the scribe shewed the king, saying, Hilkiah the priest hath delivered me a book. And Shaphan read it before the king. And it came to pass, when the king had heard the words of the book of the law, that he rent his clothes. 2 Kings 22.8-11
And the king commanded all the people, saying, Keep the passover unto the LORD your God, as it is written in the book of this covenant. Surely there was not holden such a passover from the days of the judges that judged Israel, nor in all the days of the kings of Israel, nor of the kings of Judah; But in the eighteenth year of king Josiah, wherein this passover was holden to the LORD in Jerusalem. 2 Kings 23.21-23
When they read The Law they realized they had not been observing The Passover.
Because they had been relying on The Oral Torah, the "traditions of the Elders".
What else was there?
They had lost the written Law, they had to be relying on the Oral Law later to be codified in The Talmud.
That year they observed both The Passover and The Days of Unleavened Bread:
And the children of Israel that were present kept the passover at that time, and the feast of unleavened bread seven days. And there was no passover like to that kept in Israel from the days of Samuel the prophet; neither did all the kings of Israel keep such a passover as Josiah kept, and the priests, and the Levites, and all Judah and Israel that were present, and the inhabitants of Jerusalem. 2 Chronicles 35.17 + 18
And please note it doesn't say they had not been observing The Days of Unleavened Bread, which lasts for 7 days.
If they were not observing The Days of Unleavened Bread how could they be observing The Feast of Firstfruits / The Pentecost?
The 50 day countdown was to start when The Priest offered up the wave sheaf the day after the Sabbath which occurs during The Days of Unleavened Bread.
Scripture never says they were not observing The Days of Unleavened Bread or that they had forsaken The Feast of Fristfruits / The Pentecost.
It only says the forsook The Passover, the 14th of Abib.
The Passover is the 14th of Abib, not the 15th as The Jewish people are doing now.
They call the 14th "Passover Eve".
The Feast of Unleavened Bread is from the 15th to the 21st.
When The Priests found The Written Law they read Leviticus 23:
These are the feasts of the LORD, even holy convocations, which ye shall proclaim in their seasons. In the fourteenth day of the first month at even is the LORD'S passover. And on the fifteenth day of the same month is the feast of unleavened bread unto the LORD: seven days ye must eat unleavened bread. Leviticus 23.4-6
They were not observing the 14th then, and they are not observing the 14th now.
Because they are following The Oral Tradition instead of The Written Law, The Torah.
The only way they observe the 14th of Abib / Nissan now is The Fast of the Firstborn during the daylight portion of the 14th, which mourns the death of the firstborn of Egypt who died the middle of the night before, the night of the 14th when The LORD passed over Egypt.
Remember the days begin at sunset in the Bible
The lambs had to be killed at the very end of the 13th / beginning of the 14th.
The LORD passed over Egypt in the middle of the night.
The people stayed in their homes during the nightime portion of the 14th, as commanded by God.
They gathered in Ramses during the daylight portion of the 14th and they left Egypt on the 15th, the night to be much remembered, the day after The Passover.
And they departed from Rameses in the first month, on the fifteenth day of the first month; on the morrow after the passover the children of Israel went out with an high hand in the sight of all the Egyptians. For the Egyptians buried all their firstborn, which the LORD had smitten among them: upon their gods also the LORD executed judgments. Numbers33.3+4 A person has to look to The Torah, the first 5 books of the Bible to make sense of it all, looking at what The Jews are doing now will lead a person to forsaking The Passover.
In King Josiah's day they realized their mistake after reading The Written Law and they observed both The Passover and The Days of Unleavened Bread:
And the children of Israel that were present kept the passover at that time, and the feast of unleavened bread seven days. 2 Chronicles 35.17
These days The Jews are observing The Days of Unleavened Bread for 7 days and calling it 'The Passover'.