What speculations? We have what was handed done straight from those who were there and who knew the facts. That's not speculation it's the oral transmission of facts as stated by those who were there. That's called testimony when presented in court. Given some of the Apostles and those they taught were still alive when this became tradition based on what people who were there stated, there was and is no reason to not believe the witnesses. If that's speculation, then there is no such thing as testimony. Either testimony regarding what Christ has done in your life is really just your personal speculations, and testimony in a court of law is just personal speculation, or what was passed down from witnesses who were alive at the time is not speculation but testimony by eye witnesses.
I completely understand that those who have relied on interpreting Scriptures for themselves and building their own personal religion need to have their comfort food, though. Until about a decade ago I didn't realize that under a thin veneer the vast majority of non-Catholic teaching is heresy or convenient rationalization. Hopefully you'll come to recognize that same reality before it's too late. Regards