Hello Boris,
The validation question you describe was addressed in the PDF Association publication: https://www.pdfa.org/wp-content/uploads/2017/07/TechNote0010.pdf, Implementation limits for integers in PDF/A-1 (A001). At some point, veraPDF has adjusted its validation of implementation limits for integers (PDF/A-1) based on this publication.
In short, in your case the numeric value -32768 uses a syntax of an integer and thus is validated against the implementation limits of integers, which are from 2,147,483,647 to −2,147,483,648.
I note that this issue is specific for PDF/A-1 and does not occur for PDF/A-2 and higher, as the implementation limits were relaxed for PDF/A-2 and 3 and even removed completely from PDF/A-4.
Thank you for the clarification. Very helpful!
Bye, Thomas