Season 7 onwards
1 - The TV writers do not care about such nomenclature anymore. Objectively there is no "correct" answer, because we're not "accurately guessing what the writers think".
2 - Yara took the Iron Fleet, then Euron built his own fleet. Euron's fleet then smashed most of her fleet in a surprise attack. Only a handful escaped.
Lest we forget from the books, ships also get captured - frequently when a fleet gets "defeated" the ships themselves are taken and switch sides.
Functionally, we're dealing with "Euron's Iron Fleet" now...though assuredly Yara will build another fleet in a matter of days on a show like this.
The nomenclature is...academic. Write about both in this article. Just as Davos and his son were pointing out in Season 2 that the nomenclature of "Royal Fleet" gets confusing in a civil war. --The Dragon Demands (talk) 02:45, May 8, 2019 (UTC)