Protected by Portuguese law these individuals were questioned as arguidos or as far as Operation Grange was concerned, as persons of interest.
I believe that like CB their names were brought to the attention of investigators as a direct result of following through the evidence represented by their phone activities.
Part of police procedure is exonerating persons who might be of interest, releasing investigators to progress to the next stage of the inquiry, until there is nothing left to investigate.
In 2014 the interviewees were eliminated from the inquiry. Which is not a failure but part of the process. But importantly the case progressed down other evidential avenues which are still being investigated in 2023.