Use a single cookie, storing timestamp as its value

controller/controller.php

@@ -96,8 +96,8 @@ protected function set_board_announcement_cookie()
 		// Get board announcement data from the DB text object
 		$announcement_timestamp = $this->config_text->get('announcement_timestamp');
 
-		// Set a 1 year long cookie
-		$this->user->set_cookie('ba_' . $announcement_timestamp, '1', time() + 31536000);
+		// Store the announcement timestamp/id in a cookie with a 1 year expiration
+		$this->user->set_cookie('baid', $announcement_timestamp, time() + 31536000);
 
 		return true;
 	}

event/listener.php

@@ -108,10 +108,10 @@ public function display_board_announcements($event)
 		));
 
 		// Get announcement cookie if one exists
-		$cookie = $this->request->variable($this->config['cookie_name'] . '_ba_' . $board_announcement_data['announcement_timestamp'], '', true, \phpbb\request\request_interface::COOKIE);
+		$cookie = $this->request->variable($this->config['cookie_name'] . '_baid', '', true, \phpbb\request\request_interface::COOKIE);
 
 		// Do not continue if announcement has been disabled or dismissed
-		if (!$this->config['board_announcements_enable'] || !$this->user->data['board_announcements_status'] || $cookie)
+		if (!$this->config['board_announcements_enable'] || !$this->user->data['board_announcements_status'] || $cookie == $board_announcement_data['announcement_timestamp'])
 		{
 			return;
 		}