1. If your Prod Year is custom list, then create a module with custom list dimension and a year formatted line item. Fill it with FY23 in this case.
Then in target, use formula: Source Module.Data[LOOKUP: New Module.Mapping]
2. If your Prod Year is native time, then value will automatically aggregate in Target module and sum/lookup is not required.
Himanshu's answer is spot on!
I would just like to add that Anaplan Time behaves in this way because each member of the time dimension is treated as discrete member - This is how the PREVIOUS, LAG etc. formulas work only with Anaplan Time. Members of a normal dimension are contiguous and can be summed against.