Accuracy, precision, and reliability are three completely different things. The two tests are equally accurate, they are both +-400. The Taylor kit is more precise, i.e. it will tend to give the same result on the same water sample each time, while the SWG will tend to give different, but close, readings each time. The Taylor test is also a bit more reliable, it will tend to work in nearly any situation, while the SWG salt meter can be horribly wrong when the cell plates are scaled, the plates are worn out, or the water temperature is way out of range.
In this situation, what matters most is what salt level the SWG is seeing. If the SWG level is out of range, it won't work, regardless of the actual salt level. The Taylor test is primarily useful for checking to see if the SWG is totally wrong, i.e. something is going wrong with the plates, and not useful for other purposes. Since the two agree within the precision of the tests, the SWG is working correctly, and all that matters is what the SWG thinks the salt level is. If the two measurements get further apart, then we start worrying about the SWG being scaled or wearing out.
