Car collector extraordinaire Bruce Meyer defines the acronym CSX as Carroll Shelby Experimental

That is what I thought it was too, but after reading Shelby Cobra Fifty Years, the author Colin Comer, expert in Cobras, defined CSX as Ace car company 3rd series (a =1st b=2nd c=3rd) S was for Shelby, the customer... and X was for export.

So, what is the right definition? I'll have to get the Shelby company, or the SAAC to let me know, and settle this.