Relations that are seldom or never signaled

[Manfred Stede]

The discussion on relations seldom/never signalled reminds me of the
reverse question: Are there relations that are always signalled?  A
personal hobby of mine is CONCESSION, for which I'd be particularly
curious to hear about unsignalled examples.
(My guess being that the cognitive load of the CONCESSION operation,
which I think involves overwriting default assumptions, is too high to
be triggered without an explicit instruction. Hence, an "empty" marker
such as 'and' doesn't suffice - yet the relatively unspecific and
"somehow contrastive" 'but' can signal the CONCESSION.)

Do people have thought on this?
Manfred