The VC were SUPPLIED from the north; they lived in the south. Later in the war the NVA came down the Ho Chi Minh trail to infiltrate the south for the final push - first in ‘72, then in ‘75.
They lived and did fight in the south but were recruited from the north.
NVA came down the trail in force also in May 68 for the Saigon offensive affectionately known as Mini-Tet. We kicked their ass as good in May as we had in February.