Google's John Mueller said on Twitter that when you merge or split a site, it is "essentially creating a new site." So that might mean, that if it is a substantial enough site merge or split, that Google may decide to treat the site as a brand new one and maybe some of the legacy signals might not carry over?
Here is what John said:
Merging or splitting sites doesn't result in something you can exactly determine ahead of time. You're essentially creating a new site.
— 🍌 John 🍌 (@JohnMu) May 11, 2020
The more you know.
Forum discussion at Twitter.