Hi Nathalie;
PowerSoft - the original creator of PowerBuilder - started uniquely naming their libraries by release starting in version 4.0. Sybase continued that standard as well as SAP through & up until the current version 12.6. I don't foresee Appeon changing that format either when they take over PowerBuilder from SAP very soon.
The big caveat with older PB releases - other than not being supported - is that they may not be compatible with either the DBMS and/or MS-Windows version in use by your client today.
FYI: I currently run 3 versions of PB on my development PC's (12.1, 12.5.1 & 12.6).
HTH
Regards ... Chris