Suppose I want to write an application that displays some prices of products. I discover a link using hypermedia which is a HTML form that takes product name as an input. I bookmark it and proceed to embed that link into the client.

Is there a reason why HATEOAS client should re-discover that resource (and underlying forms) again instead of using bookmarks? 

Aren't those URLs supposed to remain intact (including form semantics)? Is it less work to rediscover newly evolved API (and guarantee compability) than to keep the old one working?