(never executed) in the execution plan

I just encountered something like this in an execution plan:

->  Hash  (cost=19865.48..19865.48 rows=489 width=12) (never executed)
      Output: ly.total_count, ly.customer_id
      ->  Subquery Scan on ly  (cost=19864.50..19865.48 rows=489 width=12) (never executed)
            Output: ly.total_count, ly.customer_id
            ->  HashAggregate  (cost=19864.50..19864.99 rows=489 width=4) (never executed)
                  Output: orders_1.customer_id, count(*)
                  ->  Seq Scan on public.orders orders_1  (cost=0.00..19847.00 rows=3500 width=4) (never executed)
                        Output: orders_1.id, orders_1.customer_id, orders_1.order_date, orders_1.amount,
orders_1.sales_person_id
                        Filter: (date_part('year'::text, (orders_1.order_date)::timestamp without time zone) =
(date_part('year'::text,(('now'::cstring)::date)::timestamp without time zone) - 1::double precision)) 


The above is only a part of the execution plan and represents a derived table that is outer joined to the main table.

Postgres is correct to not execute this, because the condition in the sub-query will indeed not return any rows.

I can see why the Hash Aggregate and the Hash Join nodes can be marked as "(never executed").

But why does the Seq Scan node have the "(never executed)" as well?

I can't see how Postgres could tell that the condition won't return anything without actually doing the Seq Scan (there
isno index on the column order_date) 

Thomas