this is a hold over from the old CARB laws that began in the 90's when the first round of "smog check" included vehicles from 1968 (i got failed in 1996 for not having a breather that connected to the aircleaner).
if you look thru the catalog (or edelbrock's) you'll see "50 state legal" products for newer cars that are subject to emissions testing.
basically to sum that up: say i have a 77 cordoba. legally i can't drop on a offy 360 and afb because they aren't CARB approved components. even though they are fine and run the same and do the same stuff-- they didn't apply for testing ($$) and pay the state ($$) to get the certifications. however, edelbrock and holley did jump thru the hoops and i can pop on a performer and whatever holley that has the diamond number that is compliant (1 i think?), and if the smog guy squawks about it (they ususally don't) then i show him my paperwork that says it's fine and dandy and we just go on about our merry little day eating avocado toast and drinking michelob ultras.