Make an identity card before taking notes
Record the production company, city, venue, director, opening date and the date you watched. For a film, use release year and directors. For a cast recording, add label or edition where available. Put these details at the top of your notes so that an observation about one production never becomes an accidental claim about every version.
Look for one primary and one independent record
A theatre programme is useful for credits and a dated review is useful for what an observer remembers seeing. Find both where possible. A programme printed before a run may omit a late replacement. A review may miss the formal billing. If the two differ, record both rather than quietly choosing.
Save enough detail to locate it again
For archival sources, capture the collection title and item number. For a database record, keep the event URL. For a comparison with a recording, note the timestamp and edition, since opening logos and studio cuts can move the clock. A screenshot is a useful reading aid when allowed, but a traceable citation gives the next reader a route to the source.