While Amber Heard did testify on The Sun’s behalf in the libel case, the judge ultimately rules that her interests in that case were not identical to that of The Sun.
K and the U.S. are not the same, so a win in a libel case there doesn’t necessarily mean the same thing to an American court.
Basically, Johnny Depp may have had a day in court that dealt with this same topic, but he hasn’t had his day in court against Heard specifically.
The judge also pointed out that free speech rules in the U.