Google My Business for Company with 10+ Offices?

I started in a new company as a Business Development and Marketing Coordinator. One of my projects is to consolidate and manage all the Google My Business listings for the company. Right now I am having trouble going about it.

I have gained access to 3 locations, but I now get an error message saying "No More Ways to Verify". How do I work around this?

Also, when I fix the error above, should I continue finding every location and simply click "manage this listing"? Should I be using the "Group" feature?