If it is unclear whether the correct version of the FTS-index is being used, open SynAdmin and navigate to the tab "Full-Text Search". In a row at the top you can find the server URL, the server version and the schema version. If one of the latter is not correct, the expected version will be displayed in red font as in the screenshot below.

Incorrect schema version due to an outdated FTS-index web application

Correct schema version
Whenever the schema version of the FTS-Index is either unknown or different than expected, every creation or recreation of a subindex will cause a warning in the WebOffice log file (to access the log file see chapter Logging Properties Tab or WEB-INF Directory).

FTS subindex creation with an unknown schema version

Warning message in log file