Segmentation violation confirmed by building v3.39.20 a DOS binary. Shows very similar error to v3.33.02 with the uncompressed ZDBSP code. However, it can start vanilla doom until a level is loaded. Attached the patch for v3.39.20 so others could repeat the test.
Also, attached patch to build the Eternity v3.33.02 DOS version with support for the uncompressed ZDBSP map format. This shows an error like in v3.39.20 where loading the zdbsp maps. Attempted several tries to debug and it is possible to modify code to load a vanilla doom map, but there seems to be many places in the zdbsp code which conflict with the DOS memory system. An above post has further details.
From testing in the older Windows versions of Eternity, the map format is not necessarily the only incompatibility in zdbsp style maps, so I think Zdoom-LE is an alternative in Windows 95. It should be possible to port features back to Zdoom-CL, but there are other features in recent maps which suggest Zdoom-LE as a better choice.
Current maps, including those listed as Boom compatible, should be tested against clients other than zdoom and its derivatives. The alternative is to have other doom ports continually porting zdoom code back into their clients. This limits the ports in pursuing their goals and results in a single thread of engine development.