You only see a very few number of the settings for memory. There are actually many dozens of settings. So what you think might be compatible memory, might be, or it might not be.
The only way to be sure that memory is going to work for your motherboard is to buy a single kit of all new memory that is certified by the company producing the memory to work with the brand and model of motherboard that you have. Any other option is a crap shoot. It might work, and it might not work. Or it might work sometimes, and not other times.
You can always try to mix the memory. But if it refuses to boot, or does boot, but later the system locks up, or if it stops booting soon after mixing the memory, its probably going to be a real headache for you.