Seemed to have lost all notifications/subscriptions on site

Not sure how this happened but about a week ago all existing users lost their subscriptions (groups, nodes, etc.) on one of our production sites. Since then there have been a lot of new users and content posted. New users are autosubscribing correctly.
When I look at the notifications, notifications fields, and notifications events tables in the DB, it looks like they only contain the new subscriptions for new users. I am assuming that the tables got truncated accidentally.

So, I would like to know how to address this. I see that I have these options:

#1. Use a DB backup to append to the existing notification tables

Find a known good backup with the notification tables data and append/insert all of these records into the existing notifications tables. This is preferable since it should also pick up subscription/notification opt outs and changes they made.

#2. Edit each user's subscriptions by hand.

For each user, edit their subscriptions and subscribe them to each group, content, etc. Somehow also subscribe them to each of their posts. We have a few thousand users with N groups and X posts. This would be painful.

#3. Write some PHP to pragmatically add subscriptions/notifications for each user

Basically, create the notifications, notifications_fields, notifications_events tables records for users that do not already have records in the table - including each group for which they are a member. Maybe there are some APIs/functions in notifications that I can use to help with this. This approach would force every user to be resubscribed to all their group content/postings. This seems daunting, too.

Are there any other alternatives?

I would prefer to use Option #1, but will it work: just insert the old records into the existing tables? Could this result in some orphaned records that will never get cleaned up?

Thanks for the help!