Yes, you can combine multiple RAM kits from the same model and brand.
Yes, you can combine multiple RAM kits from the same model and brand.
You can purchase multiple identical RAM modules, like the example you described. Whether this creates compatibility concerns depends on your system's requirements. XMP profiles and DIMM slots are generally designed to handle multiple sticks, but it's best to ensure your motherboard supports the required speed and configuration. For performance, using multiple sticks can improve stability and throughput. If your system supports it, buying in packs of four or more is fine; otherwise, a single pack might be sufficient. It's important to check your motherboard specifications beforehand.
A RAM stick doesn't understand the idea of RAM kits. Adding four sticks from the same box doesn't matter if they're in one package or separate ones. The main benefit of buying a boxed set is that the manufacturer pairs the sticks for consistent performance. However, four identical sticks will perform very similarly, so you won't notice any difference.
Enthusiast ram manufacturers have the annoying habit of changing the chips used in a module with otherwise the same name. If you buy all 4 at the same time, you're probably ok but there is still some risk they come from different boxes of different batches. Especially if you buy them at different times, they may not be identical any more. It might still work the same, but there is increased chance of problems especially at higher speeds or tight timings. Corsair for example have versions on their modules, but there is no way to check without looking at them.
Certainly, you're right. It seems the setup might not be functioning properly and likely only works under default deceleration settings. The labels don't really indicate compatibility, as chip makers differ greatly and matching isn't assured. On the positive side, it's sometimes feasible to combine completely different RAM modules after some time and effort—often rewarding you more than purchasing a pre-built kit.
I think some folks say you can't mix RAM too much, but it usually works fine. If they're the same brand and model, about 99.9% of the time it functions properly, even with different chips—same chips, same model, and brand—it's around 99.99% reliable. I'm not surprised when 99% feels more than enough. The real challenge will come with using four sticks instead of two and having to align the timing precisely. That’s where the problems will arise.