How is it possible to have a collegiate chapt, & collegians from diff universities?

[CutiePie2000]

Here is a question for you all. How is it possible to have an NPC collegiate chapter & have collegian members from different universities? It's always been my understanding that an NPC chapter on a campus has collegian members only from that university.

So: The University of Washington chapter of XYZ sorority can only have women in it who are enrolled at University of Washington,
the USC chapter of XYZ sorority can only have women in it who are enrolled at USC, etc.
I am sure that you catch my drift.

I happened to be looking at an AGD page http://agdah.tripod.com/collegian.html for their collegiate chapter out in Halifax, Nova Scotia. I should clarify that Halifax is not a big place, yet, it has many universities concentrated in that town:
Dalhousie, St. Mary's University, Mount Saint Vincent University NSCAD, and Dal Tech.

I happened to notice that their webpage said:
"The Collegian Chapter of Alpha Gamma Delta in Halifax is called the Alpha Eta chapter. This chapter was founded in 1932 and since that time has enjoyed a long life on the various campuses around the city. Our members are from all of the Metro University campuses - Dalhousie, St. Mary's, Mount Saint Vincent, NSCAD and Dal Tech Together we form the beginnings of the bond of sisterhood that will be with us throughout the years.

My question is..how is this possible? In some cases, will the national allow a chapter to have members from different universities, if the town is small? I personally don't have a problem with it, but I was just sort of wondering about that.

For example:
In Waterloo, Ontario, Wilfrid Laurier University (WLU) and University of Waterloo are LITERALLY across the street from each other, but oddly, there are 2 separate Sigma Chi chapters, one for each university, because I guess they aren't permitted to have guys from both campuses in one chapter.
Also, there is KKG at U of Waterloo; and then there's DG & Alpha Phi at WLU and those women's groups are not permitted to recruit from the "other" university, only their own.

In Vancouver, BC, there is both UBC and SFU. I have heard of some UBC men's groups accepting SFU guys as members, but never of SFU women joining the UBC women's groups....