Does the ISBN prove that the thesis has been distributed to book stores?

Does the ISBN prove that the thesis has been distributed to book stores?

Unfortunately not. The ISBN (International Standard Book Number) only gives a book a unique means of identification. A book cannot be searched for or ordered in a book store until it is listed on the VLB (German directory of available books). This list confirms the distribution of a book in book stores as outlined in Sect. 19 (4).