Isn't it its context that decides the meaning?
Most of my books define 'should have ...ed' as:
(1) regret toward something undone, unfinished.
eg.
I should have asked him first.
(2) present presumption of a past event.
eg.
He should have arrived in Montreal last week.
But none of my books mention your 'presumption-of-not-so-long-time-ago' theory, Clive...