OK. I'm plowing through a lot of issues with the putative 2.11BSD reconstructions I've done to date. I keep finding things dated too new to be right. And it turns out that a few patches "snuck in" when the patch 80 catch up was done. I've outlined the ones I've found so far at https://bsdimp.blogspot.com/2020/08/missing-211bsd-patches.html but I'm sure there's at least one more. There was much ambiguity over /usr/new and /usr/local that lead to some of these, but others look like they were in the master tree, but never formally published that have all the hallmarks of legit bug fixes... I've also detailed the issues in going backwards. 2.11BSDpl195 had a different .o format than 2.11BSDpl0. And to make matters worse, its assembler couldn't assemble the assembler from the initial release, so I had to get creative (using apout, thanks to all who contributed to that!). I've also blogged about how to walk back a binary change when the old programs no longer build on the new system. I think I got lucky that it was possible at all :). https://bsdimp.blogspot.com/2020/08/bootstrapping-211bsd-no-patches-from.ht… has the blow by blow. There are a lot of steps to building even a normal system... Let alone walking through the minefield of errors that you need to do when stepping back... And neither of these even begin to get into the issues with the build system itself requiring workarounds for that... But anyway, I keep making "ur2.11BSD" tapes, installing them and fixing the issues I find... While much information was destroyed in the process, there's a surprising amount of redundancy that one can use to 'test' putative tapes. Warner P.S. ur2.11BSD is from urFOO in linguisting, meaning the original FOO that's been lost and which some amount of reconstruction / speculation is offered about it. Still looking for a good name for the reconstructed 2.11BSD release....