Corner Portfolios efficient, example, provide, needed, amount

dontknow1987

Are there an unlimited amount of Corner Portfolios on the efficient frontier?  I think I’m a little confused as to how you come up with corner portfolios.  An example in the book says that “seven corner portfolios provide the information needed to trace the efficient frontier.”  But once you have the efficient frontier, couldn’t every spot of the frontier constitute a Corner Portfolio?   Thanks