It's suspected the game was built off Portal 2's branch, but CVAR's do expose a "L4D2C5" reference.
For binaries relevant to the study of strings and CVAR flags, this repo contains very lossy Ghidra decompiles under the following setup:
1. CodeBrowser -> Edit -> Tool Options -> Decompiler -> Analysis -> UNCHECK "Eliminate Unreachable Code" (we want everything)
2. Used AutoHotkey with "Next Non-Function Ctrl+Alt+N" to recover 5000+ UndefinedFunctions that contain crucial CVAR data
Also known as "Go To Next Instruction Not In a Function". Bind "F" is "Create External Function".
https://ghidra.re/ghidra_docs/api/ghidra/util/UndefinedFunction.html
https://github.com/NationalSecurityAgency/ghidra/issues/2507
3. Headers created for each with "Function Tags" included
Ghidra decompiles align pretty nicely to the open Source SDK code:
Note that the error "The Navigation Mesh was built using a different version of this map" should be ignored -- it doesn't prevent the NAV file from working, even if the game's jank sometimes feels like it didn't load. It is not necessary or helpful to make a DLL edit that ignores outdated NAV files, and while the Source SDK does define and set "m_isOutOfDate", it doesn't appear to ever be used.
To snugly fit "client_mapkit.dll.c.txt" under the 25 MB Github limit, all lines containing "this + " (50574 lines total) were deleted -- this is a decompile, all of those lines didn't provide any useful CVAR information even with their context.