HertogJan: It depends on which entries you have in your library.
The Witcher 3: Wild Hunt
This one has 16 installer files for the main game, 3 for HoS and 6 for BaW.
The Witcher 3: Wild Hunt - Complete Edition
This one has 22 installer files.
Some months ago I installed the Complete Edition with offline installers and had no issues.
Thank you for taking the time. I probably just hit a weirdness in the download. The exe i downloaded yesterday was the GOTY installer. I downloaded what is posted there right now, and it is a different exe, specifically, the correct Wildhunt one for those of us who got the game before the GOTY and Complete editions existed. Other .bin files had to be re-downloaded, as well (10 to 15) because the posted ones yesterday were GOTY files.
All sorted now. You are gold, fellow human. Thank you again.