In another post asking about new things added to biomes I asked Valheim on Twitter directly whether an entirely new generated seed was needed, or if a copied seed would work and they said

"Most things will be available in an old seed without any problems, but there are other stuff that will only be available in unexplored areas, so it depends on how much you have explored."

Upon hearing that then this thought occurred with Sunken Crypts because that's the case with tar spawns with its biome, so it and Burial Mounds start to become explored upon entering them. With three people in three Crypts of five in the area we got around 360 iron each back in May iirc. In one Crypt at the entrance room with three branches one hallway was a dead end three way split blocked off upon mining through the mud scrap covering each rubble cave in, the middle entrance branched off two ways and then one route linearly for a good handful more, and the right entrance route went linearly down with close to a dozen rooms with mudpiles galore

It may be all in my head, but it seems as if the "dungeons" get progressively more complex as you explore new ones.

There is a large swamp island in my world that has at least a couple dozen sunken crypts. It appears that each new one I unlock and explore is larger than the previous one.

If this is a thing, I can only imagine what my 50th sunken crypt will be like.

Originally posted by Derpy Catface!:

It may be all in my head, but it seems as if the "dungeons" get progressively more complex as you explore new ones.

There is a large swamp island in my world that has at least a couple dozen sunken crypts. It appears that each new one I unlock and explore is larger than the previous one.

If this is a thing, I can only imagine what my 50th sunken crypt will be like.

Definitely in your head. I have gone from huge crypts to some that only have one room.

Maybe I'm just overly curious about how the game generates sunken crypts/burial chambers.

I would assume they are procedurally generated (kind of like how Warframe builds each mission by stitching together rooms randomly) vs. randomly chosen from a list of prebuilt dungeons.

With that said, I hope the devs give the dungeons a little love in the future. After a certain point, there is no reason whatsoever to go into a burial chamber, and there was NEVER any real reason to go into a troll cave.

Purely postulating, but i think it's random.
Have had games where the first swamp i found had few crypts and/or little to no iron in them.
My current game, always been solo, made after H&H, saw the first swamp i found containing 15 or so crypts, with the first two crypts alone containing about 190 iron