First I would try to improve the look of this model a bit. Only small changes but important I think.
There’s a few relationship and tables scattered around where I think you can organize this more intuitively.
Check out these setup tips.
Still having a hard time getting a true read on what’s required here as can’t see and test the model myself.
I can only add a few suggestions based on a model I have around this also.
See how the below it setup
You’re pretty much there but I would position tables like this.
This is what exchange rate table looks like (I think this is pretty similar to yours)
Once you have a model like this you can use a very simple calc to get the current years exchange rate
Exch. Rate = AVERAGE( 'Exchange Rates'[Exchange Rate] )
Eventhough this is average as there is only one exchange rate every day it will basically just retrieve that singular result.
Then all you need to do for last year is this.
Last Year Exch. Rate =
CALCULATE( [Exch. Rate],
DATEADD( Dates[Date], -1, YEAR ) )
I believe the using the model here is key.
Does this help you solve things?