on such a rare accasion you may with this technique indeed run into problems. the v1 of course cannot in none case be lower than actual vmcg. on lightweight like in the other thread said a derate may help.
the idea of calling v1 early is that when you at the exact v1 speak out "vee one" you are actually slightly above this speed finished the call. thats why many carriers replaced this call out with the callout "go" speaking it out at the actual v1. and this means- starting speaking go means we go.
but thats hairsplitting , there are some margins in it .generally when v1 is at or very close to vmcg it might be a good idea to abort until positivly above vmcg. 99,99% ever tried a go with an engine failure at exactly vmcg=V1 whenever on a simulator, so barely anybody can say how a real 737 on a snowy runway will handle at such a situation- and it might be not pretty.