After being blown up, Rumsey Plumb says to Bret, "Ya know Maverick, I've been shooting locks off express boxes for twenty years. That's the first one that shot back." The problem with that statement is there was no lock on the strong box. The hasp is visible with no lock in it several times. The first being when Shotgun is putting the bomb in the box. When he opens the box he puts the bomb in it and puts the box back under the drivers seat. He never took off or placed a lock on the box.
It's hard to imagine how long it would take to finish a railroad with 5 men standing around and one guy driving spikes. Railroad lines were constructed by hundreds, and thousands of workers in those days.
When the brothers discover the sticks of dynamite with the burning wick, all they have to do is snuff out the wick. They don't need to throw the dynamite and run like scared rabbits.
Miss Goodin offers each Maverick brother one thousand dollars per month for life. Shortly after, Bret does some maths, asking the executor what 50 plus 50 times 24,000 is ($2.4M). The correct sum would actually be ((50+50)*12,000) or (50*24,000) either of which comes to $1.2M. If each brother gets $1,000 per month, that is $12,000 per year or 50 x 12,000 over the next 50 years, or $600,000. Between them they would receive $1.2M. The executor should spot the mistake, as should the brothers - or indeed the writers.