So, I wanted to see how far could I progress in the beta. Albeit harry25th.txt states that just the first mission is included, in practice, you can try checking all 4, albeit you might have to gradually unlock access missions or hex-edit HARRY.CFG. As shown in a video uploaded by me last October, I could finish the first two missions, plus M3Z1 and M3Z2. I couldn't progress from M3Z3 due to the start position being wrong, and also wasn't familiar with debug features (e.g. level skipping), so I stopped there.
Recently, I wanted to see if the problem in M3Z3 could be fixed. I (eventually) approached Malvineous, who not just found how to fix the problem in HARRY.-0, but also figured out debugging features.
He added information to these Wiki pages:
https://moddingwiki....en_Harry/Cheats
https://moddingwiki....Halloween_Harry
Even with the fix, there still appeared to be 3 more unbeatable zones, named M3Z4, M4Z1 and M4Z3. Hence, I made use of the beta's "PINE_GAP" debug mode for skipping zones while recording a second play-through video, just for missions 3-4. For the ones not familiar with the name:
https://en.wikipedia.org/wiki/Pine_Gap
Using the aforementioned mode also had the side-effect of enabling invincibility. With all of these, I could manage to beat the game. Missions 3-4 also looked less finished in other manners. In particular, this covered the turtle and sentry droid found in mission 3 and the apparent repeated use of a single tile set across a whole mission (for each of missions 3-4). Another example (I think) was very few specific creatures not yet being implemented (with other ones possibly being present), at least in mission 4.
I considered making an archive with the fixed M3Z3, but since other zones are still unbeatable, I'll wait in case Malvineous and/or other people come up with solutions. Either way, the fix of M3Z3's start position involved modifying HARRY.-0, changing a few bytes at offset 0x318C02 from 4D 00 28 00 to 4C 00 2D 00.