Kiwi, JIMO,
1) If the results of 6-month follow up were apparently negative (eg, p˜1), I would present the results now.
2) If the results of 6-month follow up were apparently positive (eg, p < 0.05), I would present the results now.
3)If the results of 6-month follow up couldn't say either way, I would cancel the presentation and wait 12-month follow up result.
They just might have not had enough time to analyze the data though.
Or failure of embargo policies...