Exactly. There is no way in hell all of this is somehow supposed to turn into one, unless he writes some incredibly vague and awkward dialogue that could be interpreted in each path's way.
Take it with a grain of salt because I haven't followed the development that deeply anymore but:
The explanation, and how
I understood is that, while you as a player can only see and decide for one "ending" or decide to outright ignore certain scenes or the erin stuff during the game (femboy and sissy fetishes is not for everyone), after the timeskip Mars has done all the events with the girls and erin you haven't saw in the background/meantime anyway and will converge.
So effectively you have a 100% playthrough after the timeskip going forward for the main stuff, with a bit more favor of the person you chose before the timeskip I guess, if you want to or not. We need to wait and see if he will pull this off in a coherent way.
Act 3 aka after timeskip won't be very long according to the dev and very different in overall mood.
Also for you guys who are expecting happy endings should steel themselves. The dev seem to be averse to a classic happy ever after and thats fine.
I mean not that they are not happy but they will be very nuanced. The harem one especially.
However I am highly anticipating the finished product and I just love Nitro's art. Next update is gameplay stuff....which is long overdue. The dungeon and mini games have so much potential and can add to the quality of the game. It will also add variety to the mostly VN styled game as well. Hope he will pull this off.