My wife is waiting for me to be gone for a few days. I have rapidly glanced through what you wrote. I don't have a great deal to respond with.
Couple quick answers - No I don't know when the Bible was published. If Maria Van Siclen's marriage date of 1814 is accurrate, then it would have been published prior to 1814. I don't know which Eastling first owned the Bible but assumed it was Luther and Maria Van Siclen Eastling. The last owner was, according to a letter by Violetta Voorhees Ferdinand Eastling, a son of Cornelius Eastling who was a son of Maria Van Siclen.
Individuals who aren't willing to accept the data with the bible as factual can easily say even after the Bible is discovered that all of the entries were made after the Bible was found.
As to sources of names Van Siclen versus whoever. There too anyone can make any source mean whatever the individual choses to create for the name. There are no absolutes in Genealogy.
My name is Gusman, my fathers name is Gusman, his fathers name on the grave marker is Gushman, My grandfater had a son who spelled his name Guzman as does all of this descendants.
So because I have an Uncle name Guzman and a father named Gusman, is my name then not Gusman? My father had two brothers both of who retained the name Gusman. Because they are Gusman does that make me the son of either of the Gusman brothers or am I the some of my father Gusman.
I can also go through the same play on names for the Eastling descendents.
My point in the preceding is that I always make a point in my family lineage to apply the last known confirmed spelling of a name available to myself. In the Maria Van Siclen situation the last recorded spelling is Maria Van Siclen.
At one point and for many years the Eastling descendents of Luther and Maria for years spelled the name of Maria Van Siclen as Maria Van Sickle. A spelling which I used until Van Siclen was discovered in the Violetta affidavits. I then switched to earliest known spelling.
About the letter about 10 years old..do you know if the inquirer had uncovered the Violetta Voorhees affidavit wherein Maria's bible entries are included?
I must go,...I will again review your posting when I return.