Android Contacts: Is it possible to reference a given contact entry using a URN?

Let me try and clarify my intentions.

I'm developing an app that accesses to the Android contacts provider. I have already implemented a mechanism for pulling contacts from the contacts provider and storing the results in an SQLite table. Currently, when I query for the results of a contact's _ID, I can retrieve all the data for that contact, phone numbers, email addresses, etc.

However, in order to specify which of those my app should use on future occasions, I have to store the resulting contact data (e.g. CommonDataKinds.Phone.NUMBER, CommonDataKinds.Phone.TYPE etc) in the SQL table.

This presents a problem if the data in the Android contacts provider has changed. One solution I have considered is to re-query the _ID and store the data that has changed. However, implementing such a solution requires gathering all data for that contact, making it difficult to determine the correct contact data to use.

My question is thus:

Is there a unique record key used in the Android Provider's contact data, in the same way as there is in the Provider's contact entry itself? A phone number or email address equivalent of Contact._ID?

Failing that, does the Android contacts provider store the last modified date and time? I'm hoping that if I can't reference the contact data in the provider, I can at least run a check to see if anything has changed since the contact was selected for use in the app, allowing my app to alert the user that the data has changed.