Hi.
Typically stability studies are part of the pilot production validation, so yes - it's normal that the test units come from a yet unvalidated line. However, in such a setting the pilot line and the production process are expected to be qualified first and controlled within the limits that the line is supposed to be validated under. If successful, subsequent production will have to be controlled within the same, established limits.
The main point is that stability is (hopefully) established for a given production setting and a given set of controlled parameters settings (accounting for all the rest, which is noise, too), which is maintained for routine production later. Otherwise it's just anecdotal.