For the purposes of determining novelty, a prior document should be read as it would have been read by a person skilled in the art on its "relevant date". The relevant date of a previously published document is its publication date, and that of a document within the meaning of Art. 54(3) EPC its date of filing (or, as the case may be, priority date) (Guidelines G‑VI, 3 – November 2015 version).
According to the boards' established case law, for ascertaining the disclosure of a document forming part of the state of the art within the meaning of Art. 54(2) EPC, the relevant date is that of publication (see T 205/91, T 737/00, T 1162/07). For the purposes of examining novelty, a document is to be assessed from the perspective of the skilled person on the publication date, T 305/94. Interpreting a document using knowledge which only became available to the relevant experts between the publication date of the cited prior art and the filing or priority date of the application to be examined or the patent in dispute is an issue relating to inventive step, not novelty (see T 205/91).