When you say that: >>> "however the DES share price had already fallen to 13.5c BEFORE the sell recommendation." <<<
It had been around the 17c to 16.5c mark for at least a week and a half prior to that, with a slight downturn just prior to the tip (some leaks perhaps, that a sell tip was imminent?) ... the day prior it might have dipped to 13.5c, but it actually closed at 14.5c :-