Cataloging tips - False use of copyright date

In the case of a publisher/author using false copyright date, how can cataloger be sure about the validity of copyright date?

Of course this always a possibility, But, at the cataloging stage, it is not our responsibility to verify copyright, only to record information we have. RDA does not rule on what to do if we know it is false (probably because in many western countries like the US, copyright is not automatic and must be applied for). So, it is better to record it as copyright information (representing the resource as it represents itself) but then use a note to explain that it's known to be fake. It frequently happens that the copyright status is valid but the date is false. Commercial publishers will often do this when they publish something towards the end of the year. They will often put the following year as the copyright date, to give the content more "currency". Again, if we know the date to be false, we still record it as the copyright date, but then use a note to record actual date.

Cataloging tips - Confusing copyright symbol

If publisher use the @ symbol followed by year, for example @2018 in the copyright area, can we assume that the @ symbol is meant to be © symbol?

Yes, if it is clearly associated with a copyright date.

Cataloguing tips - Confusing copyright date

A book copyright-ed in 2010, then reprinted and copyrighted in 2018. Which date is used to determine the correct copyright of the book? Should both dates recorded on tag 542?

Simply to record the information the resource gives us. Generally would record the latest date in the 264, and then you can record both dates in the 542. Note that though 542 is a highly formatted note and you need to ensure you you use the right field. $g (for copyright date) is not repeatable. $f could be used if there's a statement on the resource that includes both dates. You could use $n (note) otherwise.