Even at the poles you can get more than 4 at any time. You can solve for lat/long with 3, but you need 4 or more to solve for lat/long/altitude. You are actually also solving for time in both cases (number of range equations equals number of unknowns, for those that are interested in the math. At least that’s the academic way of looking at it. In practice its done with matrix equations and least squares, for those interested in even more complex math).
Perhaps the info you have is dated to when the constellation was not built out. There are almost always 30 to 32 GPS satellites up and running at any time these days.
I have not been to Antarctica yet, I was repeating hearsay from soneone who went there. When I go I will fer shur have GPS since one million-acre slab of snow looks pretty much like any other!