Storing notes after the trial?

On some levels, the answer to this is going to vary based on where you are living and where you do your work. Ultimately though, no matter where you are living, it's essential to keep your notes readily available at least until there is a final transcription made.

At least until the final transcription has been made, approved, and turned over to the lawyers or the court, but it's a good idea to have them available - and to be aware of the requirements in your state.