1. Does it mean GD’s conviction is overturned? No. That’s a matter for the Court of Appeal.
2. Will the Court of Appeal do so? Probably not. There are exceptions for evidence gathered lawfully at the time, which becomes unlawful due to “subsequent legal developments"
This is more difficult. Does the state fail this test when it knows that there is a CJEU judgment striking down the underlying EU law? The timeline matters here.
In April 2014 (DRI) the Irish state knew data retention was on very shaky ground. In December 2016 the CJEU confirmed national laws were covered by this principle (Tele2). In April 2017 the state received a report from...
It seems to me likely that more recent convictions could be challenged on this basis. Your guess is as good as mine whether the SCt would agree, and where the cutoff date might be.