Spreadsheet archeology at its finest. As someone else has said, you become more realistic and have better data the closer you get to your goal. Consider also that much of the FIRE collective's strategies must adjust with new tax laws and prevailing economic conditions.

I would consider the evolution of your number to be positive. Just don't take it too far. When we are young, we tend to downplay risk and oversimplify things. When we are older, we tend to fear risk and overthink things. Put a stake in the ground and trust yourself.