Martin Senour products ARE Sherwin Williams. Not just "made by" Sherwin Williams, we are talking exact same product with a different label on the can, same batch code, same exact product.
But this is all a moot point because the products that are used in production aren't even available to repair shop or anyone else as a rule. They are applied in a way that no repair shop could apply it, they are different products.
The manufactures have accepted products that they recommend, from every manufacturer who has spent the time and money to get that ok. When I was a rep for MS I had a book with all the products oked by the big manufacturers like GM and Ford, a list of Dupont, S-W (MS) PPG, Sikkens, products.
Now, that all being said, applying a PPG primer over the OEM Dupont paint isn't a problem at all. Even applying your Dupont paint over the PPG paint that was painted on you car 10 years ago after an accident. That really isn't an issue at all.
Applying a product over a different manufacturers fully cured product isn't a big deal, it's insoluble (if it's a good product) It's when you are asking the products to intermix, like a clear over another brand of basecoat, that is a HUGE no-no. The base isn't fully cured or dried even, and you are applying another clear over it, not good.
If you are mixing products, what tech sheet do you follow?
HOWEVER, you "can" do it, hell yes you can.
Pro's who know WHAT these products are can get away with it, for instance you are spraying a paint over an epoxy primer of a different manufacturer you follow the tech sheet on the epoxy primer and then you follow the paint's tech sheet as it may refer to spraying over THAT companies epoxy primer. This isn't "that" big of a deal, but it is opening up the door a little bit for trouble.
Your typical quality shop is going to use the same products start to finish, they have a warranty provided by that company BECAUSE they are using all their products. The painters have been trained by them, their products are all that is in the shop, and for this they get a life time warranty like at the shop I work at.
Does it mean the shop isn't a good shop if they mix some products, no not at all. But as a rule, as a rep, funny things often happen in those shops, we called them "Junior chemists" and they had problems, OFTEN. It wasn't so much that they used a different primer or something, it was that they were VERY open to making their own rules, the different primer by it's self wasn't a issue, it was that opened a door, that was just an example of the other hair balled things they did.
If you want to eliminate issues, if you want your project to go as smooth as you can, you stick with all the same products as they are suggested on the tech sheets.
For the home hobbiest, follow the tech sheets, use all the same products from one line and you are going to be WAY better off.
Brian