How accurate are proof house's numbers?

[41 Colt]

I was looking at some Colt SAA guns online and some that the sellers list as 1898 manufacture appear as 1897 on the proof house site. Is there another reference for Colt numbers?

Proof house lists the Colt SAA cutoff as 174999.

 

[Skinny 1950]

I have been using this list...it seems to confirm what you arrived at:

http://www.coltparts.com/Dates_of_Mfg.html