The answer is really easy, SCEA handles the NA Store and SCEE the EU/AU Store. SCEA can't upload things on the EU store. We had DLC problems with the game Rocksmith 2014 there it was the same. NA had all DLCs within 3 weeks, we Europeans had wait 6 months to get the same DLCs.
Yeah, I think the reason why there have been delays in the release of the weekly DLC for PS4 users within SCEE's region (and I could be wrong about this) is down to SCEE's quality assurance (QA) processes.
SCEE manages content for the Middle East, Africa, Oceania, as well as for European countries. SCEE calling themselves 'SCEE' is actually quite misleading. They cover something like 100+ countries al in all. Anyway, what this means is, all games and games content has to go through SCEE's QA process in order to be released within a country or territory administered by SCEE (e.g. to be released in Australia or in Russia); however, if some of the games, or game content, submitted to SCEE does not pass QA due to regional variances (for example, some countries or territories have much stricter censorship laws/ requirements than other countries might have, such as say, in comparison to the UK), content will not be released by SCEE. It will fail QA and the developer will have to re-submit. Unfortunately, the QA process by SCEE can take an interminably long time.
I suspect that the Triss costume DLC is in QA with SCEE and SCEE are attempting to determine whether this content can be released within SCEE terrirtories on the whole, or whether it can only be released for some countries within SCEE's remit but no other.
Of course, and as I said, I could be completely and hopelessly wrong....