The other thing to consider is that SP and P/E ratio at any...

The other thing to consider is that SP and P/E ratio at any particular point in time is also a matter of demand/supply of shares available at that point of time..ie..the if long-term holders are in a large proportion, that creates the SP and P/E to climb up more than it would if it was the other way around.
P/E ratio also depends on what is generally the market sentiment to that particular industry or sector of the economy, and it also depends on the sentiment of global markets.
Also, usually P/E ratio is the highest when a company is in its early years, (and earnings are low, but expectations of growth are high)...as earnings increase, generally P/E ratio drops lower unless there is expectation of even higher growth rate.
So as such P/E ratio is not very scientific, and a ball park estimate must be made..that's why LOM could be an apt assumption pre production for a mining company, even though there exists so many other variables as mentioned.(and it will change over time)