[chockablock]

Official rules say otherwise: "Each puzzle includes at least one “pangram,” which uses every letter."

https://www.nytimes.com/puzzles/spelling-bee -> click on 'How to Play'

[tptacek]

I've always assumed they generate the puzzle starting from a pangram.

[spyspy]

That's exactly how it works. The script scanned the dictionary for pangrams and then built the puzzles from that list, filtering out pangrams that didn't meet the other rules for the game.

[ddejohn]

This is the assumption I started with when I started building my clone.