(feel free to move this post if you think it should go elsewhere)
This topic got me thinking that it would be useful to have a guide on how to convert content from arbitrary old versions, including old DOS Lemmings .lvl and .dat packs, definitely for individual levels, and, if possible, for bulk conversions, too. Right now you kinda have to track down the conversion instructions for each intermediate conversion you need and it's a bit of pain, and I've been wanting to go through some old levels on an old hard drive that never got NL conversions, as I'm curious if any of them would be salvageable (I'm guessing no, and I want to see if I'm right). Even recently, it took me a while to track down the instructions on how to cleanse levels on an nxp.