1. Go to any page in the TimedText namespace: https://en.wikipedia.org/wiki/Special:AllPages?namespace=710
2. Enter into your console mw.config.get('wgRevisionId');

// Result is 0

3. Repeat with the oldid of the previous revision (like so)

// Result is accurate

I may be misunderstanding how these pages work, but wgCurRevisionId works just fine, so unlike the File namespace, there's some nonconcordance (e.g. stuff like if (mw.config.get('wgCurRevisionId') !== mw.config.get('wgRevisionId')) breaks down).