Robert.
There are 2 ways of saving out an archive.
1. They way you described.
2. When saving a PLA file if you take the options button, you are give the choice to save out the entire library.
If you only interested in a few library parts I would take the 1st option as saving the entire library creates large files were as saving out only the parts used in the project will considerably lessen the file size.
HTH.
Cheers.
Ben