I am conducting research with a Ph.D. scholar under a supervisor, who is, in some sense, heading this group. The Ph.D. scholar and the supervisor have two articles undergoing a second round of review. The comments received in the first round of review were fairly straightforward to address, according to the Ph.D. scholar. For this reason, it is believed that the papers will be accepted soon.
The research I am conducting can be seen as an extension of the work done by the Ph.D. scholar and the supervisor. For this, it would be useful for me to have access to the articles they have under review. However, the Ph.D. scholar is reluctant to share these articles, and would prefer to wait until they are accepted before sharing them with me. Note that the papers are not available anywhere online, not on a website and not even on a preprint server.
The question is not about what I can do: I am okay with the situation, and have no real problem waiting till the articles are accepted. I am however interested in the more general case.
I assumed that since I was, in a way, a part of this group, any research that they may have under preparation or review would be accessible to me, in some manner, and I wouldn't have to wait until the published versions came out to access the research. Is my assumption correct, and is my experience less common than the alternative?
Simply put, is it common for members of a research group, including graduate students, to be able to access articles that are under review, so that they can obtain insights to further their understanding of a topic, and hence increase the pace at which they conduct research? Or is the alternative more common? For obvious reasons, I am particularly interested in fields/topics in which preprints are not widespread, and the usual publication process holds.