Currency exchange rates are date-specific.  When entering a currency exchange rate, users can add an "as-of" date to indicate when that rate started. 

In this instance, the revenue records in question were entered prior to the currency exchange rate.  As a general rule, exchange rates do not affect revenue records from the past.  Since there was not an exchange rate that covered the periods for the older revenue records, no conversion was possible.

 

If users have access to historical exchange rates, the Currency Exchange Rate Batch template can be used to enter or import exchange rates to cover the periods needed.