Terry...my first sentence was in reference to your last sentence...
"How can they say what is STOCK on Cobras since they are not built by a manufacture? They are hand crafted."
In other words, I agree with the point you are making in asking the question. That sets up the context of what follows in the next paragraph, where I opine that it is much easier for a street cop to determine what's after-market on more modern day machinery.
Does that help you understand?
Remember, a cop has to have some cause to stop you in the first place...