Interesting. You'd think that GPGSV would show the number of satellites in view. Actually I think it shows the number of satellites expected to be in view above the horizon based on the almanac data. I'm getting a full set of 16 satellites in GPGSV when I'm inside a big faraday cage of a building. Yet GPGSA shows no satellite fixes.

The trick is that I look at the GPGSA string and if it's a bunch of blank fields (lots of commas), that means no satellites used in the fix. If I see a lot of satellite IDs in the GPGSA string then that's how many satellites are in the fix. So that's how I can count them. I'm going to try that now. :-)