Take for instance nisan 14. There are at least 7 major events that occured on this day. im not saying believe the site below, but the scriptures they give do show us that all these events happened on nisan 14.
Its obvious the pseudo events have been shaped to always fall on nisan 14. The stories would work just as well regardless of the day or month.
http://heartofwisdom.com/biblicalholidays/2010/03/01/nisan-17-odds-one-in-783864876960000000/
Nissan 17, Noah’s Ark safely rested on Mt. Ararat (Gen 8:4) Note that the seventh month was later designated as the first month at the time of the Exodus (Ex. 12:2).
Nissan 17, Hebrews entered Egypt (Exo 12:40-41) 430 years before deliverance.
Nissan 17, Moses led the Israelites through the Parting of the Red Sea (Exo 3:18, 5:3)
Nissan 17, Israel entered and ate the first fruit of the Promised Land (Joshua 5:10-12)
Nissan 17, The cleansing fo the Temple by Hezekiah (eight hundred years after entering the promised land. (2 Chronicles 29:1-28)
Nissan 17, Queen Esther saved the Jews from Elimination (Esther 3:12, 5:1)
Nissan 17, The Resurrection of Messiah (think about it)