Does 'sync (on commit)' mean the index is updated immediately?

Good Day

Environment:  Oracle 12c (12.1.0.2) on Exadata

I have an Oracle Text domain index with the parameter ('sync (on commit)'.

Does this mean the index will be updated immediately when say a new document is added?

Here is the CREATE script:

CREATE INDEX BLDOCINDEX ON BL005_PUBLISHED_DOCUMENT(DOCUMENT_PDF)INDEXTYPE IS CTXSYS.CONTEXTPARAMETERS('sync (on commit)');

I had a user in our Test environment add a new document and then try to do a search on some key words and the search didn't return the document he had just created.

I am an Oracle Text newbie.

Are there any other reasons the document was not returned even though it contains the key words?