Ok, I would err on the side of caution and say the ones that say MG E-Liquid on them are all ready mixed and indeed not a concentrate. The easiest way to test this is to drip a bit on to the atomiser and see how it tastes. But you wont know the MG of the e-liquid...which I find problematic.
It might due to call the brand on the label, or shoot them an email and ask for them to clarify what the heck they are (send pics?)