Authority Source Text (in either Spanish/Castillian or Catalan/Valencian) Text in English Myth Reality
Valencian Autonomous Government

Statue of Autonomy, article 7.1 Los dos idiomas oficiales de la Comunidad Autónoma son el valenciano y el castellano. The two official idiom of the Autonomous Community are Valencian and Castillian. This "proves" that Valencian is not Catalan. In fact this phrase doesn't imply in either way. Just like Castillian, in the same phrase, is commonly called Spanish, Valencian is commonly called Catalan.
Council of Europe

Spanish declaration to the Kililea European Union Resolution
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Spain declares that, for the purposes of the mentioned articles, are considered as regional or minority languages, the languages recognised as official languagues in the Statutes of Autonomy of the Autonomous Communities of the Basque Country, Catalonia, Balearic Islands, Galicia, Valencia and Navarra. This implies that for each Statue, there's a different language. The construction of the phrase doesn't imply that. In fact, the Basque Country and Navarra recognise the same language as official (Basque/Euskara), as well as do Catalonia (as Catalan), Balearic Islands (as Catalan) and Valencian Country (as Valencian, see article 7.1 above).
Spanish Constitution

English version of the text
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The Spanish Constitution text is available in "Catalan" and "Valencian", but the text itself doesn't mention either of these languages. The Constitution recognises them as separate languages. The text itself doesn't even mention them.
Spanish Constitution

English version of the text
N/A
See above.
If the text is available in both "Catalan" and "Valencian", they must be different languages! Since the website doesn't back up this claim, it could well be that they added Valencian as the southern dialect of Catalan. Nevertheless, the criteria of the administrators of the site for adding translations has no legal or scientifical validity.