Only 24% of Mexican crime guns trace to American FFLs
Sen. Grassley says he has the figures. The wording of his release isn't entirely clear, but it seems to be referring to 24% of guns that the Mexican government asks to be traced (which are minority of its crime guns, and certainly disproportionately those of American make). And of course a gun sold by an FFL to a honest person, and years later stolen and smuggled out, would count as a gun traced to that dealer even though his transaction was 100% proper.
So the actual percent of Mexican crime guns traced to American FFLs is likely far less than 24%, and a good portion of that may be stolen. The actual percentages are a far cry from the Administration's claims of 80-90%. But for some reason I doubt you'll read this in WaPo or the NY Times anytime soon...