The list of tag synonyms contains a column called "created". Does this column contain the date when a synonym was proposed or the date when the synonym was approved?
For example, on Mathematics Stack Exchange the tag (holomorphic-functions) is a synonym of complex analysis. When I check the list of tag synonyms (and looking at the active synonyms) the date shown there is from May 2016. However, I can see it as a separate tag in a snapshot from February 2017 archived in Wayback Machine.
Additional question: If this table shows when the synonym was proposed, is there also a way to find out when the synonym was actually created/approved? Is there some other way than checking the data from SEDE?