I heard that I'd you haven't explored a majority of your map it can still generate new new biomass after the update? Is this true?
as long has the chunk hasn't been loaded when the update occurs any chunk that hasn't been loaded can have a chance to generate with any of the biomes which are available to the game. So you could get one of the new biomes, or any one of the current biomes which could be different than if you loaded that chunk today.
Caution though, from what I understand some quirky things can happen with chunk generation to worlds which are split by updates. Meaning you could be walking along and then come across a shear cliff in the middle of the desert, or some really weird glitch trees/water etc.