Contradiction with Exodus 12:18
Exodus 12:18 specifies the time to eat unleavened bread from the 14th to the 21st day of the month, whereas Deuteronomy 16:9 is about counting seven weeks from when the sickle is first put to the standing grain.
Exodus 12:18: In the first [month], on the fourteenth day of the month at even, ye shall eat unleavened bread, until the one and twentieth day of the month at even.
Contradiction with Leviticus 23:5-6
Leviticus 23:5-6 gives specific dates for Passover and the Feast of Unleavened Bread starting on the 14th and 15th day of the month, while Deuteronomy 16:9 counts weeks from starting the harvest without specific calendar dates.
Leviticus 23:5-6: In the fourteenth [day] of the first month at even [is] the LORD'S passover.
Contradiction with Numbers 28:16-17
Numbers 28:16-17 sets the Passover at the 14th day of the first month and doesn't reference harvesting like Deuteronomy 16:9 does with its agricultural focus.
Numbers 28:16-17: And in the fourteenth day of the first month [is] the passover of the LORD.
Contradiction with Leviticus 23:15-16
Leviticus 23:15-16 starts the count of weeks from the day after Sabbath during the Feast of Unleavened Bread, differing from Deuteronomy 16:9 which begins counting from when the sickle is first put to the grain.
Leviticus 23:15-16: And ye shall count unto you from the morrow after the sabbath, from the day that ye brought the sheaf of the wave offering; seven sabbaths shall be complete:
Contradiction with Exodus 23:15
Exodus 23:15 mandates the observance of the Feast of Unleavened Bread but does not connect it to the agricultural calendar like Deuteronomy 16:9, which directly ties it to the harvest period.
Exodus 23:15: Thou shalt keep the feast of unleavened bread: (thou shalt eat unleavened bread seven days, as I commanded thee, in the time appointed of the month Abib; for in it thou camest out from Egypt: and none shall appear before me empty:)