Here's a possible solution:
In 1822 Morriss was handed a "trust" of sorts, so in essence he became the executor of a secret trust with certain terms attached to carrying out of that trust. In the event that he could no longer manage that trust he was to pass this duty on to someone else who was capable, which he eventually does.
In 1862 Morriss passes this secret trust onto the unknown author and in doing so there are certain terms attached to this arrangement as well, one of those terms being a period of twenty years, this new arrangement thus ending in 1882, at which point the new executor (unknown author) was to distribute the wealth as agreed.
So in 1882 a lawyer in Richmond believes that he has been charged with the duty of executing a wealthy secret trust that he can't even find, nor can he find the heirs of that trust. So what to do? Hence - three years later you have the Beale pamphlet in 1885.
Now I know all of this sounds a bit crazy, and is a bit crazy, but is it really a condition that's too bazaar to exist? The evidence suggest otherwise.
We have to remember that Morriss was simply a third party safety valve in the event that something went terribly wrong with whatever plan/agreement that was already in place. Since Morriss was never contacted in regards to the box in his possession by the time the original 10 year term had expired we can only assume that his services were never required and that the original plan had ended successfully, thus the services of Morriss were never required and he was simply left out in the cold. Remember, Morriss was only promised a share "if" his future services were required, which they apparently were not.
Now many years later Morriss still believes that he is in charge of something that no longer exist and in living up to his previous promise he passes this charge onto someone else, this new executor being our unknown author, and he too firmly believes that there is actually something left to be administered. So, at the end of these new terms, in 1882, we have yet another individual firmly believing in something that no longer exist, "hidden wealth" if only he can find it just as he has been charged.
Now all of this sounds too crazy, I know, but in 1882 there exist a suspicious exchange of letters between an aging attorney and another individual that may actually prove otherwise. This attorney would have been intimate with many of the people Tat and I have already discussed in these forums. This is why those private collections become so important when conducting research, because nothing is truly ever a secret if it really existed among men.