ANSWER
Short answer.
An ISBN identifies a published book; a repository deposit makes your thesis findable through the university. Your university may require the repository workflow even when an ISBN is optional.
01 · ISBN
What an ISBN is used for.
An ISBN identifies a book or publication. It does not automatically meet a university repository requirement, so check whether your university requires it, recommends it, or leaves it to you and your printer.
Settle the final title before requesting one. ISBN.nl says title metadata should align with the title on the cover.
02 · UNIVERSITY REPOSITORY
What the university needs for digital publication.
Your university may need a digital copy, a licence agreement, a specified file format, metadata and sometimes an embargo decision. Put this on the same timeline as printing, but do not assume the printer completes it for you.
At UvA, candidates provide a digital copy and permit publication through UvA-DARE using a licence agreement. Leiden also requires a digital version and non-exclusive publication licence before the defence deadline.
03 · ORDER
When to request an ISBN and submit repository files.
Confirm the approved title page and required text. Then decide whether you need an ISBN, complete the relevant printer or publisher details, and prepare the repository version and licence agreement.
If an embargo, copyrighted chapter or data restriction is involved, ask the library or graduate school before approving the proof.
SOURCES
Official sources.
Your university’s current regulations, Beadle’s Office and graduate school make the final decision on requirements and ceremony details.
ISBN.nl: title metadata guidance ↗UvA Library: Publishing a Doctoral Thesis ↗Leiden University PhD Regulations 2021 ↗