Two items that seemed to be missing from the walkthrough posted earlier.
After you've done the researcher scene where she is in a cow bikini, there is a customer in Succubus First on weekends who is interested in cosplay. You'll need to go to the Research Lab and talk to the Sadistic Researcher (not sure if you need to finish his other quests), then work for three Fridays at the Lab. Return to Succubus First and talk to the cosplay fanatic, then schedule On-Site work.
Once you've advanced Logistics, the old man in Succubus First will give you a promotion guide. After you've done it once, you need to talk to him again. He will appear at Logistics and give you a more advanced copy of the book.
I am not sure if these are strictly necessary for the True End because I also missed the Executive on my first pass.
This game was also excellent. Hope it gets a proper translation and a decensor eventually, what a joy to play.