The value-date attribute of an value element is not marked as required in recent IATI versions at iatistandard.org (for example transaction value -> value-date).
To perform currency conversion correctly, and hence, cross IATI source comparison, this date would preferably be required. I'm interested to know everyone else's opinion on this.
In the old docs it was marked as required. Which makes me wonder if it was made non-required on purpose.
I also checked the IATI 1.04/1.05/2.01 xsd schema files, the value-date attribute is missing there for most occurrences of the value element.