A contact isn't shared, why not?

There are a number of reasons why this may be the case:

a) Once a contact is added or edited in your address book it takes some time for it to be processed and added to the private graphs of your connected contacts.

b) Contacts marked as "archived" or "do not share" are never shared

c) If a contact's data includes profanity it is likely that it will not be possible to share the contact