Your assumptions are very close to correct. Even though one was supposed to attain a great deal of knowledge in a chosen field, the acquiring of special knowledge that makes one unique does not occur until the doctorate level. Many professors assume a mastery of existing knowledge before you even enter the study hall.
Depending on which institution and which science, the dissertation or the thesis can take on different names and purposes. The more accurate term for a doctorate level dissertation might well be “book.” Practically, one is authoring one’s own book of knowledge on the subject.
In the education field, a thesis is put up on the shelf only to be perused by other entrants into that line of study. It becomes part of the special section in the Library Hall. With the introduction of the digital recording this library now spans far past the physical college shelves.
It is an honor for a work to be used as a college textbook or to be cited by another student because this is often how one’s work gets to see the light of day. Do not take this wrong, a dissertation and a passing grade is the entrance into the doctorate field, and the professor or an understudy will read every word of a work, but self-publishing may be the only way it receives wide attention.
Only teachers in my field have heard of the Nongraded Primary Education by Gausted or the Christian Look at the United States Revolution by Rasmussen. All material is keep at the university. I was in the era before the rise of the internet so all my studies and theses are in written form, and I have now no desire to digitally transcribe them.
My assumption is that the more physical sciences and the doctorate liberal arts also store, keep, and compile their information the same way. Some with the budgets have subcontracted companies to come and scan all their work into the college intranet, but this is only with the huge institutions, and with works that receive a higher acclaim than the average dissertation.
I hope this answer was satisfactory as I did not think I would get to it on this ML King holiday in which I do so much community service work for our fellow men.