I'm not so familiar with US flights, but in Asia and Europe I expect to be able to tell what the flexibility on my ticket is from the endorsements and travel dates.

Refundability is a completely separate issue from flexibility - it is perfectly possible to have flexible, non-refundable tickets, or, for that matter, inflexible but refundable (for a penalty) tickets.

If my ticket does NOT say "valid flt/date shown" and then I expect to be able to use the ticket (subject to availability in that booking class, but in any case on a standby basis) at any time within the boundaries of the "Not valid before" and "Not Valid after" fields on the ticket.