I once had a pit owner hand me a copy of his "contract" to sell X million tons per year of gravel for a wind farm project. It too was going to sell out in five years. I checked and no such contract existed. Hype was this liar's middle name. I'm now a creditor on the bancruptcy filing, as is another appraiser. Ya gotta check it all out.
I'm sure this goes without saying, but if BV is part of the scope of work and assignment, I would clearly say so in the report. All over the place. If the biz walks or never gets going in the first place, RE is all that is left standing. As for royalty rates, you might be surprised at how many leases are in place. Aggregate is heavy and doesn't travel far. 30 miles is about as far as it can be shipped. Meaning there are aggregate pits and quarries all over the place if you look. Pit operators would much prefer to not tie up money in owning minerals if they can lease them.
I get nervous when I see anyone using the retail value of cleaned/screened product. I once followed an appraiser's $15 million dollar value with one less than $1 million on the same thing. He had totaled the "net" after expenses retail value of the product, but had failed to discount it, or to mention the net was part of the BV and only a part of it earnings to the RE.
RE interest is entitled to only the royalty from the mineral lease, plus PV of the reversion. Everything else flows to the biz.
As to the reversion, figure out what the HBU would be today if vacant and available and that's as good a value as you will get. Normally, it's way out there in time (20 to 30 years), so PV of the reversion at anything approaching a double digit rate (comes from Sales, just as TS says) isn't much. In your case, it is.