How many unique puzzles are there?

[JMike]

I am starting to notice that I'm repeating some puzzles. The evidence is that I'll do a puzzle in a certain amount of time, and the fastest-solvers grid shows me solving it faster.
I don't know whether that means I've played all the puzzles and sometimes I get a faster time on one than when I played it before, or whether puzzles get picked at random, or what exactly is happening.

So how many are there?

Thank you!

[admin]

Just under 75,000 unique puzzles - but they are spread evenly between difficulty levels and feature combinations (i.e. regular, + capitals, + market towns, and capitals + market towns). If you play only a certain combination of difficulty level and feature you will exhaust the available supply quite a bit faster. Which combination do you tend to play?