The problem in this case wasn't the third party data, but an error in how that data was analysed and presented. By all accounts the raw data from the telecom companies was both complete and correct.
Maybe in this specific case the telecom data was correct, but can you assure the same for every datum ever provided?
Trusting telecom data is essentially the same as trusting an eyewitness.
The eyewitness says the truth sometimes, but you can't trust them as an infallible source of truth.