You have a 50-50 chance of it working even if the timing and everything else is identical. There are always chances for memory not to want to work correctly with each other even with same models if they are bought at different times and different kits. I would say 30-50% chance of unmatched kits working properly, and 70-90% chance of a kit from same vendor and model working together that haven't been tested in shop to work with the other modules. Like when I bought my 64gig kit it was crazy expensive but I wanted to make sure that I got a kit that has been proven to work together.