I use scoping studies, PFS, DFS, BFS to value companies now and...

I use scoping studies, PFS, DFS, BFS to value companies now and their potential.
Some companies have 50+ years resource. It would be ridiculous to work an NPV for that full LOM.
20 years is pretty standard and what I revert all studies to if its over.

I always use Post-Tax figures to keep everything uniformed. This is how I value companies.
The more years used, the NPV can be greatly skewed.
I'm sure everyone has their own ways to value companies but I feel this DFS is not as good as it looks.

Get the Post-Tax NPV and revert it back to 20years.
Taking 8 years from its most profitable years off and going Post Tax will smash the NPV.
The NPV is going to be nowhere near the 1bn mark.

You can then use your own NPV to determine when its a good time to buy.
Generally 20% NPV pre funding and 40% post funding is what a lot of people use as a rule of thumb as fair value.