Is the ltrim and rtrim necessary? SQL ignores trailing spaces when comparing string columns, if you have leading spaces it's probably better to clean up the data if possible.

If you can get rid of the functions (they're often used where not necessary), then use not exists or not in (the left join is slightly slower usually). Also consider that there's a behavioural difference between not in and not exists when nulls are involved (on non-nullable columns they perform identically)

p.s. You don't need a DISTINCT in an IN or NOT IN subquery.