Here's the part that doesn't seem right to me.
"This date corresponds to Nisan 14, which was when Jesus held the last valid Passover."
In Matthew 24 Jesus tells us when the "end of the age" and the destruction of the temple will be. Until the end of the age and the destruction of the temple all Passovers were valid.
Read Hebrews 8:13 "...ready to vanish away" Something that is ready to vanish away has not yet vanished away. And did not vanish away until the destruction of the temple in 70AD.
Peace