The gun companies are like the car business in one respect, in that the different levels of employees who work in the business may change companies now and again.
While non-competition and non-disclosure agreements aren't uncommon, it's also not like the companies are going to be disseminating all kinds of knowledge, let alone about everything, and definitely let alone anything proprietary, throughout the companies. It's not uncommon (or unreasonable) for information to remain contained within the departments where it's needed, and not shared among other departments in the company.
People in
training and
sales may not have the depth of the info possessed by the
repair technicians, but not all repair technicians may know as much as other technicians, either. I've known of long time, experienced repair techs who seemingly spent more time working on things with
engineers, than they did at a warranty repair bench.
People in production may just be assembling things, working in production "cells", and not require specific knowledge beyond assembly and bench checks to confirm normal assembly & manipulative functioning.
Just like any other business where goods are designed, manufactured and produced.
Another thing to to consider about a "working, functional" finish is that it may well be the result of having received a lot of feedback, and requests, from major end users who have their own preferences when it comes to specifications ... like non-reflective, non-shiny finishes. Making such things standardized across a product line is sometimes a good idea, making it more efficient for manufacturing and production.
Of course, the RTF/RTF2, reportedly (according to Glock) designed to satisfy a request for some specialized military users who wanted a grip texture that would better adhere to gloved hands, didn't exactly meet with a rousing success when it was produced for regular regular commercial guns.
Then, there was that ambi G21SF mag catch. Ugh.
But a finish, though? Something that meets the needs of the variety of bulk/contract purchasers, and which satisfies any requirements for hazardous chemicals used in finishes, and is sufficiently utilitarian, seems to be what the major makers are gravitating toward.
Sure, some have also adopted PVD or Cerakote finishes, at least as options in some of their models or model lines. I don't doubt but that if a major vendor decided to place an order for 20K-25K Glocks with a specific slide & barrel finish, that Glock would quote them a price and fill the order.
That's how the original green frames came about, some years ago, and we've seen grey now, too. (But adding color to a plastic is easier than setting up, or outsourcing, a plating process, isn't it?
)
In the meantime, the rest of us are pretty much at the mercy of whatever cosmetic finishes the gun companies decide is the right combination of practical, utilitarian and feasible (financially).
People buy Glocks, regardless of whatever current finish is being used. (We were recently told they're currently running on a 24/hr manufacturing & repair schedule, and are now producing up to 100K guns per month.)
I've got Glocks with different finishes, myself. It actually makes it easier to identify a couple of visually, when they're in the safe.