Letters like F1, S1, BX and IBL on a pack describe how the seeds were made, and they matter for how consistent the THC will be. An S1 is a plant selfed to itself and tends to be uniform, while an F1 is a first cross of two parents with more vigour and more variation. The glossary on https://potentthcseeds.com explains each code with examples from their THC seeds, which cleared it up for me. Stable codes are the safer buy for a small grow.
