Since I'm working my site's upgrade in background, I decided that I'd handle as many of the data changes in the current Drupal 8 instance as possible to both stop the bleeding and try to reduce the need for a large data migration.  As I mentioned in my previous post,  I had a few different flavors of blog posts spread across 5 different content types.  Merging them together was relatively simple. At first I was planning on writing code to handle the work but I found contributed modules that could do the job. Disclaimer, I did this in a sandbox, do not try this in a live environment. 

Here's what I did:

• Added functionality so notes can optionally use titles.
  • Added a flag to the Note content type to indicate whether the title should be persistent and used.
  • Updated my call to hook_node_presave in a custom module to only autogenerate the title if the flag is not set.
  • Updated the twig templates to display titles if the flag is set.
• I added a source field to the note content type in case I need it for the future.
• Merge category taxonomy vocabularies 
  • Each blog type had its own separate category field and its own unique vocabulary.  I used the Taxonomy Manager module to move terms into a single vocabulary.
• Converted content from each content type into note
  • I used the Convert Bundles modules to do the heavy lifting.
    • The mapping tool worked perfectly.
  • I merged them a content type at a time populating the source based on the feed.

All this worked perfectly and this site now has 1 blog content type, Notes.  When it's time to move this to Drupal 9, I'll probably rename the content type to Blog Posts.