Legit Holley jets are stamped after determining where they flow in comparison to a specified high/low range for a given jet #. As such, jets that both fall within the same #'s range can have a different hole size, yet still be rated the same.

Holley used to offer some "close limit" jets that were refined in their ratings even more. If you see a #602, that's a #60 that flowed in the middle 3rd of the acceptable range for that size. The BLP and MaxJets are rated by .001"-incremental size and are even more refined.

I bought some Jeg's house-brand jets recently to fill in a couple of sizes I was low on. One size measures slightly smaller compared to the Holley of the same #, but the Jeg's jets have an obvious bevel on the entrance to the hole that the Holley doesn't, so they very well could flow the same. On the other hand, one of the three sets of Jeg's jets isn't even sized consistently between the pair. The smaller one doesn't appear to have been machined all the way thru the hole, so I have zero faith they flow the same, much less that they are rated correctly as a Holley replacement. Don't think that I will be buying any more of those...