I have been involved in formulating many of the recent Kodak black-and-white film developers (T-MAX, Duraflo, Technidol) so I offer these comments:
Commercially produced branded chemicals are different from the generic published formulas for several reasons. The published formulas are made available to help those that wish to to mix their own processing chemicals. The materials listed need to be widely available. The manufacturer may have an unique in-house component that works better than the generally available material so the in-house material is used.
The goal of the commercial and published formulas is to provide SIMILAR photographic results. Identical is a lofty goal. Identical results are not achieved in photographic products. With careful examination there are ALWAYS differences.
Also, the performance requirements placed on a commercial product are stricter than mixed-at-home product i.e. storage tolerance, tolerance to a variety of water contaminates, manufacturing requirements, etc.
A manufacturer may have a proprietary ingredient that will improve the product's photographic performance. This is the case with most if not all Kodak chemicals as well as Ilford's ID11 Plus.
Manufacturer's may also include a trace material to aid in identifying the source of the chemical product. There are instances where counterfeit chemicals have been detected and also cases where there are complaints on chemicals when the chemicals were actually made by someone else.
Component measuring isn't an issue for photochemicals. It is a greater issue in film emulsion manufacturing where accuracy is even stricter. To deal with parts per billion accuracy there are two totally separate approaches that are both needed. Purity of the components and addition of tiny amounts.
There are some components in film at very low levels that help performance. If the level is increased it will totally destroy the film's performance. Mercury is well known for this. It is immaterial whether the Hg comes from a measured addition or is an unintended contaminate in a raw material. The most accurate way to deal with this is to use nearly Hg free materials and then add exactly how much you want to be present.
This is easier said than done. Mercury and other contaminants to AgX are present in many required components so it has to be removed. In "the old days", (1970's) some known contaminates were required to be present in the raw materials. This meant that gelatin from animals that were fed specific food were required to make a specific product.
For addition there are multiple chemical preparation and addition workstations. The workstation that is used depends on the handling requirement i.e. worker safety, contaminate characteristics, and of course material quantity. For parts per million additions there is a separate weighing and addition station that is used to precisely and accurately makes additions.
This is described in: makingKODAKfilm.com