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I believe that Google ranks your pages on the basis of what they deserve with minor modifications.  All of my sites have double listings where they are strong.  Some have triple or quadruple listings where they are outstanding on multiple facets of a topic. There are no "tricks" to getting these.  You need content that answers the query, there can be multiple ways of answering the query, and your content needs to blow the competition out of the water.

Link reclamation for the client as well as the top competing websites. This can be a lucrative way to build up natural link profile, and obtain "new" links on older domains. I usually run Cognitive SEO with top three competitors, view links that are shared  and which are lost vs. live. This is an easy way to reach out to previously interested parties as well as build updated relationships.

Thanks, we'll check all of the old URLs are redirecting correctly (though I'd assume given the htacces and WP settings changes, they would). Will also perform the other check you mentioned and report back if anything is amiss... Thank you, Lynn.

Sounds like you've found the issue, or at least the main one. I would wait on the dev site to be removed before starting over with a new domain. KJr