I'm not exactly sure what VGC is, but l am going to say EVs will always be on a Pokemon, and will never be lost, unless used by an EV dropping berry.
Whatever VGC may be, if by "cutoff" you mean Limit, than it will not gain EVs because you have to gain experience when EV training, or it won't count. lt's the same concept as training a Lv 100 Pokemon, it won't gain EVs.
I hope this answers your question or at least makes a better understanding for you. ~