My field is that of communication, so when I talk about reliability and credibility I talk about both concepts in light of a message, of a source or as an outcome of either.
Of course there is a clear distinction in theory. Do people (while participating in an experiment or filling out a survey) really make that theoretical distinction? And do they still in daily life? And is that distinction measurable, or are they simply two sides of the same coin, meaning that they are perhaps two parts of a multidimensional construct?