subgenius wrote:you need to distinguish between "truth" and what people "say" is truth.
So, while people saying it was true that the earth was flat and now it is said that it is true the earth is round(ish)...does not represent truth changing...for what was true when people "said" the earth was flat is still true today. The truth never changed, just people's opinion about it.

But what you determine as truth is only ever what you decide you are going to accept as the truth.
For the people back in the flat earth days the truth was that the earth was flat - that was based on them making a decision to believe the people who put forward the idea that the earth was flat. Now, you choose (I assume) to believe the people who have put forward the idea that the earth is round, so for you, that's the truth.
What you seem to be suggesting is that what you believe to be the truth, may not actually be the truth. But on that basis, you will never get to the bottom of what the truth is, you will just develop what your opinion as to the what the truth is. Based on which statements, information, experiences, opinions etc you assign as being part of your process for determining truth.
It's a pointless discussion. The truth is simply what we decide is the truth, nothing else has any relevance. Perception is the only reality with which you interact.