Cell phone data
Just because the cell triangulation wasn't used in this particular case doesn't mean it isn't useful. I've been involved in three rescues this year in which cell-phone triangulation was either the main factor involved in finding a person or greatly reduced the search area/time. I, too, live on an Island and, whilst it's common not to have the required three cells for an accurate location (due to, pretty much always, being near the coast) two towers will give you a pretty good idea where someone is - combined with local knowledge.
Of course, none of that requires the recording of data. In both the case presented here and the ones I have been involved in, the data was taken from the moment a request was made (along with a fecking huge charge from the telecom provider - batards!) . Historical data was not required. Actually, in one case it would have been very useful but we got lucky and managed without.