That´s what I´m saying too, there is no 100% guarantee, that even the same brand and model in different packages and not in the same kit will work together.
But I think the same brand and model, even not in a kit will get an user a better chance than mixed brands and models, where the specification could be different. It´s just easier for someone to buy the same brand and model, than buy another kit from another brand and model, in which case he or she would have to compare lot more things, like timings, voltage, xmp or not,...