Only data from subjects, who have signed consent, can be retained in clinical trial documentation. Everything begins with consent and hence the subject allows the investigator to begin trial related screening processes and record trial related data . ICH E6 (R1) allows for both a screening log (8.3.20) and a subject ID log (8.3.21). ICH E6 also tells us why there is a subject ID log:- "allows investigator/institution to reveal identity of any subject". So you would need a confidential log that allowed the identity of subjects to be revealed, if needed. ICH E6 also allows different logs to be combined (8.1) "provided the individual elements are readily available". So you can combine logs for subjects who have consented.