I haven't put any effort into this since filing the Issue + talking about it there + nesdev. But here's one thing I did do today, which makes me believe the issue likely relates to both loading *and* saving in Nestopia. I tested with Genghis Khan.
FCEUX appears to work fine/correctly across the board.
Nestopia loading test: I took the 8KB .sav from FCEUX and dropped it into Nestopia's save\ directory (overwriting the existing one I had there). In Nestopia, the result was "No saved data". To me, that means there's an issue with Nestopia and loading, or with the MMC1 emulation bits somehow.
Nestopia saving test: Deleted the existing .sav file, started a game in Nestopia, played for a season, saved in-game (Other -> Save), closed the emulator and made sure the 8KB file was there. Copied that into the FCEUX sav\ directory and ran FCEUX + game: "No saved data". So FCEUX won't work with the 8KB .sav from Nestopia, leading me to believe Nestopia is also saving incorrect/wrong data to the .sav.
I did a binary file compare between the Nestopia .sav and the FCEUX .sav. There are several differences given the randomness and variance of events in the game (I've no control over that), but nothing "obviously gigantic" -- what I was looking for was to see if, say, the lower or upper 4KByte regions were massively different -- they weren't. However, one thing I did notice is that FCEUX .sav had this, consistently at this offset (referring to $1F09 to $1F0F):
Code:
Offset(h) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
00001F00 2E 00 01 00 06 00 00 00 00 11 A4 4B 4F 45 49 00 ..........¤KOEI.
While I couldn't find that identifier anywhere in the Nestopia .sav. I even tried injecting those values into the Nestopia .sav at the same offset, thinking maybe that was their simple identifier check -- nope, still "No saved data".
Finally: I will say that the "16KB WRAM" tweak proposed in the GitHub Issues is the wrong approach. I believe fixing this the proper way (whatever that may be) is the better choice. "Kludge fixes" just end up creating more work for someone later on/down the road, or make someone go "Eh? Why are KOEI games in Nestopia making 16KB saves while every other emulator uses 8KB? What is the history behind this?" (We've seen tons of evidence of this in the past few years, where people dig through FCEUX source to find "behavioural quirks" that can't be explained/justified very well. The less we do this going forward, in any emulator, the better!)