Tony Vargas
Legend
I never saw a hex mat until around 83 or 84, when I started seeing people using them to play Champions. First I saw of grid mats was with 3.0 - but that's specifically the vinyl mats. I do recall a grid/hex pull-out sheet in an old Dragon Magazine before that.The AD&D Dungeon Master's Guide was released in 1979 and includes diagrams showing how to use a square grid and a hex grid to determine how many enemies can attack a character and which ones of them you get a shield bonus against, etc. I can attest to grids being a well-known technique going right back to 1974.
And, of course, dungeon maps were almost always on a grid, and overland, hex.
So that was my experience. But, I wasn't gaming in the 70s, and I bow to your longer experience on that point.