Hmmm.. I've updated an old sheet format with a few new notes linked to custom props. After saving the sheet format I opened an old drawing (that needs to be revised) and for each sheet I selected 'properties' browsed to the new format, selected it etc.
The title block does change as in the boilerplate stuff changes, but the new notes with custom props never show up.
If I start a new drawing and change the sheet format in the same way the notes with cusom props DO show up as you would expect.
What's going on here.... it's too early for this!