Well, 4 sticks with the same model name may be different, if u are unlucky.
There is a reason for the RAM kit.
Even if the RAM is from one maker, not being in one kit,
it could be made from different batches of the memory modules,
while with the same specs, but from the different supplier,
the non kit RAM is not exact 100% match.
Even when the part number can suggest its all the same,
the non-kit RAM could be made of different manufacturing components over time.
We all know that motherboards are very sensitive to the RAM exact match,
so while it can work in many cases, it wont work in all the mobos correctly.