On the day of the assassination the DRE contacted Joannides and told him they had interacted with LHO in New Orleans that summer and had a tape of a radio debate with him. The DRE asked Joannides what should they do, to which Joannides replied to wait a while and he would get back to them. Despite this order, the DRE went ahead and published some negative articles about LHO without consulting Joannides.
The question is, why was it only on the day of the assassination that the DRE first decide to tell their case officer about LHO?
One possible explanation can be found in the below document which was discussed on The Lone Gunman Podcast back in July of this year. Here is a link to The Lone Gunman Podcast for anyone you would like to hear their discussion of the document: LINK (starts at 54 minutes):
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Here are the relevant sections of the document:


As you can see, Helms told the DRE in late 1962 that if they were to make any TV appearance that they were to notify him in advance.
This brings us on to the Oswald/Bringuier radio debate in New Orleans. At the start of the radio debate (the relevant section being at 37 minutes in the below DVP video), Bringuier was introduced as the DRE delegate. Therefore, Bringuier was representing the DRE in this debate. According to the above Helms document, the DRE were supposed to notify Helms in advance if the DRE were to appear on TV. This might have reasonably been inferred to include radio too. As the radio debate occurred quiet quick on the heels of the Aug 9th Bringuier/Oswald fight, it appears the Bringuier/DRE did not get a chance, or did not bother, to inform Helms in advance. And once the debate had occurred, the DRE may have decided not to tell Joannides about LHO at all as this would amount to admitting it had broken its promise to Helms to notify him in advance of making a media appearance.
This would explain why the DRE went to the level of sending out a press release and writing to Congress about LHO before the assassination but did not inform Joannides. The DRE wanted to maximize the propaganda from the Bringuier/LHO radio debate but could not inform Joannides as this would force them to admit they had broken their promise to Helms.
I don’t know what the official explanation was the DRE gave for their failure to inform Joannides before the JFK assassination (perhaps someone here knows), but if they never did give a reason, perhaps the premise I’ve outlined here might be a possible reason.
ALL THREE OF LEE HARVEY OSWALD'S RADIO & TELEVISION INTERVIEWS IN NEW ORLEANS IN AUGUST 1963
LINK (37 minutes):