In my $year = --$year;the decrement operator is changing the $year in the OUTSIDE scope, then assigning it to the lexical $year in the INSIDE scope (which is the one that your print statement in BLOCK4 sees). Remember, until that statement finishes successfully, the INNER $year doesn't exist.

You could get the behavior you're looking for with: my $year = $year - 1;which doesn't change the value of the OUTER $year.

Update
Added example in second para.