When an invoice/ETR is issued it has a date on it, this is the Issue Date. The issue date is very important because all calculations are based using this date and the Expected Date. For example, if an invoice dated 2016-01-01 is traded on 2016-02-01 and is not settled until 2016-03-31 then it will be outstanding 90 days (i.e. not 59 days)