You are right but the real problem with "what are the chances of getting XYZ right" is that it's the same type of question as "what are the chances of getting the right size legs to be able to stand on the ground" (Physicist's point?) Exactly. The "right" gene length is the length between a "start" codon and a "stop" codon.
And there's a heck of a lot more than one way to skin a cat.