@NathanG - Yeah, but it’s a very involved digital process. It’s not just “copy and paste.” It’s copy and paste and splice.
The exons get spliced together after the junk DNA is thrown out. This is more like grafting pieces of different texts together into a document, to extend your analogy of human transcription.
The amazing thing as you pointed out is that this process can occur over and over again without any errors. The only exception to this I think would be where there were genetic illnesses of some sort or another. In this case I suspect perhaps not all of the junk DNA would get thrown out and therefore you would have a breakdown in the process.