Legendary pastthen-v5 was made
-v6 was created and made default, v5 was dumped
-v7 was made and released before finished, v6 stayed default
-v5 was recreated from scratch and readded, v7 was made better, v6 optimised and stayed default
-
valleys was created as lua mapgen and then rewritten and added to Mintest core as new mapgen, v6 was further optimized and stayed default
-more mapgens where added such as fractals (forgot when mathgen was dumped)
-mgflat was extended and is somewhat of a complete mapgen now
new-v5, default-v6, prereleased-v7, valleys and many others are all alive and kicking
most games run with v6, some recommend or even need v7, some subgames don't care, others use singlenode and apply their own on top
I may have missed some or mixed up some of the timeline but it should give a general idea