One Million # notes are very hard to come by. I've looked for them (& ladders) for years & I rarely see them. I truly suspect solid radars are more common.
They're highly under-rated by Charlton (& collectors alike) IMO. They're like the bookends of the #1 note but don't get half the respect. Your note books at nearly1/3 the price of a 0000001 note in the same condition. Crazy b/c they're rarely offered & perhaps that's the reason they book so low (for lack of data!). I know low # are tough too.
But many of us old-timers had a similar thread on how Charlton has been a bit weak re: 1954 & DF special numbers. It's probably due to lack of data & just not updating the figures b/c they don't seem to jive with the rare occasion a DF solid (or low #) comes up for auction.