I was in a hotel kitchen once at an Aman. I then briefly saw a grid with guests names, pictures (from passport) and preferences, room numbers etc. I also once found papers left in a buggy or hotel car which had information about different guests staying, status, did they have something special included, should they get upgraded or get VIP service etc. This was at a Four Seasons. Both many years ago so the systems might be more up to date by now, but these are the specific things I have seen with regards to how they keep track.