5jjt:
You have mentioned one of the lesser-known "secrets" to flawless-looking car detailing. Many wonder why they cannot achieve having their car look like the posted photos by professional detailers of cars they detail. While it may not appear to be big deal, someone who uses a pad that was used for applying a compound and then clean it and re-use it for applying a wax/sealant Last-Step Product (LSP) may wonder why there are swirls in their car's finish. The same could go for microfiber towels.
As mentioned above, it's expensive to have product-dedicated pads (and microfibers), BUT it's also one of the things that separates the "hacks" from the truly professionals. It's also one of the reasons for professionals having or using ONE car-care manufacturer's line of products. 3D/HD is a good example of this. It's also why they use color-coded microfiber towels for specific products or have organized storage bins for specific microfibers for specific products. It's also why they may wash the microfiber towels in separate loads, never mixing a protectant-removing towel with a load of LSP -removing towels. This is one of the reasons for washing glass-cleaning towels by themselves. Hacks wonder why they can never get glass to come streak-free. Maybe they have cross-contaminated towels from washing. Attention to small details can yield better results and negate or avoid problems that plague ignorant wanna-be "hacks".
I am not aware of chemical cross-contamination between the same type of product from different manufacturers. I would use the same cotton cloth to apply Aerospace 303 as Meguiar's Protectant, even though I have washed the cloth between uses, but that's me. The same could be said about my car wash media pads/mitts/sponges/brushes. I have four different wash soaps in my arsenal, but only one set of wash media and I do thoroughly clean my media after each wash, but again that's just me.