I'm assuming that you want your calculation to be made for each account, correct?
I'd try the following:
Dimension #1 = Account Number
Dimension #2 - max Year per account:
, [Account Number]
Measure: the balance that corresponds to the max year:
=FirstSortedValue([Original Balance], -Year)
I think this should give you the desired result. If it doesn't work as expected, please create a sample app and post it here, and I will take a look.
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