The best practice here is to NOT override master page items on document pages. Build the master pages so they only contain objects which remain intact (other than changing automatically, like Current Page Number placeholders) as is on document pages. I know that’s not possible 100% of the time but it should be the goal, especially if you need to add single pages to a facing-pages spread more than a couple times.
That means:
1. Use Primary Text frames on the master pages, with NO text in them. These don’t have to be overridden on the document pages. If you insert a single page and a left-facing page ends up on the right, and you have different columns/margins for left and right, you can easily reapply the correct master and not end up with overlapping text frames.
2. Use dynamic text features on master pages whenever possible. For example, instead of typing in placeholder text for headers (which must be overridden and entered manually on doc pages), insert and format a Section Marker there (Type > Insert Special Character > Markers >) and then when a header changes for a new section, use Numbering & Sections on that doc page to change the section name.
3. For all other items that need to appear in the same location on various pages but customized for that page, create a Library item or a Snippet, which remember their locations, and base them on an object style whenever possible. Example: photo credit text frames, pull quotes, image captions, images with caption, order form, placeholder ads, etc.
AM