Google updated its core updates documentation to say smaller core updates happen on an ongoing basis, so sites can improve without waiting for named updates.

• Google explicitly confirms it makes “smaller core updates” beyond the named updates announced several times per year.
• Sites that improve their content can see ranking gains without waiting for the next major core update to roll out.
• The documentation change addresses whether recovery between named updates is possible.

https://www.searchenginejournal.com/google-confirms-smaller-core-updates-happen-continuously/562989/