After deleting all my TimeMachine snapshots I created enough real free space to continue the installation of the remaining additional mics (10 packages about 100 GB) of the percussion library.
Although the VSL Assistant will not start the installation if there is not enough real (so total free - purgeable) free space for the download + the installed library + some reserve available it does use the purgeable space during installation:
- I started with 340 GB free of which 309 GB purgeable where I could not install a further additional mics package
- After deleting the TimeMachine snapshots the purgeable was reduced to 285 GB purgeable and I could install packages one-by-one
- After installing the 10 packages I now have 241 GB free with only 1.98 GB purgeable.
So overall the remains free space seems correct and the purgeable file space has been used. How the purgeable space became so high during the updates of the standard version, which I assume overwrite existing sample files with the new smaller ones, might be investigated.