Hello again,
I apologize. For some reason, I didn't get an e-mail notification of your e-mail from 3 days ago and just now got a notification of your most recent e-mail.
There are a few points that are still unclear to me, but I think I have enough to go on.
The XPath formula to get at the corresponding field value for the group with the maximum date is:
/my:myFields/my:Table1[my:T1_accounting_year_closed = /my:myFields/my:maxDate]/fieldToRetrieve
So to get the value of the ETR_per_return field in the row with the max date, you could use:
/my:myFields/my:Table1[my:T1_accounting_year_closed = /my:myFields/my:maxDate]/my:ETR_per_return
and you can use this in a rule or Expression Box control.
And just as a tip, you don't have to have a control bound to a hidden field in order for it to work. As long as the field is present in your data source, it will do its job. So you can delete that 1px textbox for your hidden_field field.
Is the above information enough to solve your problem?