Yeah, not all remans are the same. It depends on their tier. For example, we carry Bosch starters and alternators in many of our locations, but branded under our own label. There are different tiers of products that Bosch offered us in our private label line from a very good quality that very closely meets production specs to lower quality products that did not replace everything and/or did not use as good of parts were used. Being that our private label is our "value" line meant to target price sensitive customers, we opted for a tier closer to the bottom.
We do have a premium private label line that uses tier 1 product meaning that it comes from the same factory and quality that the OE gets it from. It is the exact same part that you would get from the OE for considerably less which tells you how much of a markup the OE puts on these parts.
There is also a difference between a "production" spec part and an "aftermarket" spec part for many parts manufacturers. A production spec'ed part is what is sold to the vehicle manufacturer and an aftermarket spec'ed part is what is sold to the public. Generally, production parts have to meet more stringent quality standards(tighter bell curve) than aftermarket parts even if it is an OE part. This is why the stock OE parts on your vehicle will usually last longer than the very same OE replacement parts.