In constructions such as this,
select followed by noun-phrase implies that there is a predefined subset -- select flights is a list of flight numbers/ other flight designations specifically listed for this purpose.
selected followed by a noun-phrase merely suggests a subset that may be chosen (at an unspecified time, by unspecified selectors); even at a future date by a future selector.
Discount is offered on 'select items'. -- Specific items set aside for discount sale. One list applies to all customers throughout the sale.
Present the 'selected items' at the packing counter. -- Customers select items of their choice. Items differ from customer to customer and from time to time.