Er... I'll weigh in on the questions I can.
Don't know about The Letter and the song by the Liverpool Pub Quartet. Have never been that much of a fan of either Beach Boys version in any of their various mixes. Also, I don't have Rarities...
Can't Wait Too Long is a new edit/mix. More details on that in a separate thread appearing near you very soon.
And finally, the writer's credit for Lonely Days is given as... (unknown). Sorry!