SR redtop belts...not a noob "?"

[SR20d2fourT]

Hey guys, I already searched and found the gates number for the S13 belts
:Belts (PS, AC, alt)
Gates K050370 Alt.
K040345 PS & most AC

I thought gates numbers were universal? I called my local autozone and other shops and they didnt know what they were talking about. They were saying how they swapped the numbers around and, for instance, on the PS he was saying that it came up like this K04035 meaning he dropped the 4... he said it would be about a half an inch shorter and what not, but if this is universal why didnt this work for me? Is there any other way that a local auto retail shop would understand what I need other than having to use th Gates number? thanks guys.