Connected conditionals can be quantified by expressions such as “always” and “sometimes”. The negation of “on every occasion” is “on at least one occasion, not so”, not necessarily “never”.
For example:
“Whenever it rains, the ground becomes wet.”
“On at least one rainy occasion, the ground did not become wet.”
The second rejects the claimed universal connection.
The two concern the same conditional relation, with properly differing quantity and opposite quality. This applies the quantified-proposition principle to conditionals.