nah it doesnt affect the a/r it is just that garrett makes and / or distributes certain turbos and their components and not others.
i guess for the .86 a/r GT2871R they decided not to make the cover for the intake side anymore but people still wanted it so precision started making them.
the covers apparently are made by a casting house for precision, not necessarily in house.
i guess the exhuast side, which is labeled with teh a/r is shared between the GT2871R and other turbos, not necessarily GT turbos and not necessarily for street cars.
Garrett / Honeywell produce endless versions of turbos and i am sure a ton of the components are interchanged, similar to platform sharing by major automobile companies.