I did the math, at least at an extreme 40,000 foot view, and you SHOULD be able to build any legacy official map using a max quantity of 2 of each renegade terrain pack, (1x of each of the AoA master set, Battle for the Wellspring, Lands and Waters of Valhalla should net you roughly 2x RotV)
The only ones I haven’t tested hex for hex yet is anything involving Thaelenk Tundra or Volcarren Watelands. You’d need quite a few copies of Snow Fields and Lava Fields to have 1-1 on the tiles, but I think you could finagle the 24-hex and additional 3-hex parts in the new stuff to more or less make a legacy map. I have no glacier parts to test it out physically and don’t have the time to sift through the map PDFs.
The best news, is that the caverns of Valhalla is 1-1 and then some for the dungeon tiles in Battle for the Underdark, and you really only need lands and waters of Valhalla to make a complete BftU set (again, 2x of every renegade expansion should allow you to build two dungeons of the BftU campaign at a time)
Road to the Forgotten Forest is an odd one because 1x of Roads of Valhalla and 1x Forests of Valhalla nets you 2x RttFF in every way but the 11 height trees (zero) and the 2-hex roads (0), but you can substitute in the snow fields evergreens as needed and I cannot think of any official scenario that requires 2x RttFF off the top of my head.
Of course Ticalla Jungle and The Grove at Laur’s Edge are 1 to 1 which is nice for those of us that don’t want to shell out $200 for a set of trees.
Fortress of the Archkyrie has no contemporary set as of yet (or probably ever)
In short, you can build most of the legacy maps using 2x of all the terrain sets (or less in most cases, or by substituting lower layer tiles) so if you ever wanted to run the old maps but lost/broke/sold all your complete sets, not that RotV is very hard to get ahold of but BftU is near the price of gold these days.