An actual implicature is any potential implicature that is not canceled by its context.
The expression I think that some went has two potential implicatures:
- The matrix sentence I think ... has the potential implicature "I don’t know [that some went]."
- The complement clause ... some went has the potential implicature "not all went."
Of the two potential implicatures, only I don’t know that some went is an actual implicature, because the other occurs in a complement clause that the matrix clause does not entail. If some went were uttered independently, as a main clause, its potential implicature ‘not all went’ would also be its actual implicature.