In principle, you should be able to mix any pair of DIMMs from any vendor combination as long as you make sure all DRAM timings and clock are set to the lowest common denominator.
In practice, some combinations are problematic (particularly beyond 1600MT/s) but most still work.
I doubt a likely minor model revision would have much of an impact on compatibility. Modules with poor compatibility often fail to work even if you put all identical DIMMs in. Kingston may not make the fastest DIMMs on the market but they usually are quite accommodating. I have yet to have trouble mixing Kingston DIMMs manufactured years apart, which usually means completely revised PCBs and different IC suppliers.