There are lots of good reasons that have nothing to do with carbon for updating the soil maps, and I'll leave those aside right now. I'm just going to go really sort of lazy on you, as someone who is trying to build a market. In real life and nature we know that there is a maximum theoretical annual increase possible, and in soil carbon stocks that's about 1% per year of the background stock. If I'm trying to build a market and figure out how to monetize all the information I have, if I have a good soil map in the background, I can introduce the test well. If my calculation says it's more than 1% per year, it's probably wrong.
If I'm working in a marketplace where I have good background soil mapping, I can bring financing in because I have a sort of insurance number in the background. If I haven't seen that soil map updated since 1991, I don't have the 1% QA/QC rule that I can stick into my financing story.