I agree; that's what they call "postal history"! Sometimes the story behind a collection with multiple items like this is fascinating in itself and perhaps they ought to be kept together if that's the case. Have you been able to find out anything more about the senders, recipients or postmarks? I'm sure they have a story to tell!
Sometimes, if the recipient was well known in a small town (think doctors, lawyers, etc), the postmaster likely knew many of them anyway and was easily able to direct it. How times have changed. Nowadays we have very large street numbers and multiple people with the same, or similar, names!