Problems with DAX Date filter

Hi

I'm quite new to DAX and am experimenting with filters in CALCULATE, using a simple table of sales data containing data from 2017 to 2019 - here's an extract

Source data is at https://1drv.ms/x/s!AmxJyApgEAcYgtUghDmk57MBicCw0A

I've set up a measure to sum only order class "P" sales:

Priority Class Sales = CALCULATE(SUM(Sales[Sale£]),OrderClasses[Order Class]="P") 

and another to just sum sales in 2019:

Sales in 2019 = calculate(SUM(Sales[Sale£]),YEAR(Sales[OrderDate]=2019))

Here's what happens when I use them in a table:

Could someone explain why the "Priority Class Sales" filter works while the "Sales in 2019" filter appears to have no effect?

Thanks!