I just watched the interview Bobby Nolan gave about the bullet (fragments) he was given by nurse Bell and which he passed on to Captain Fritz's office, despite several requests from FBI agents to hand it to them.
At around 17.48 in the interview (available on You tube) Nolan remarks that his initials are on the evidence envelope but they are upside down. Earlier he commented that he initialed the envelope when he left it on a desk in Captain Fritz's office.
What I find puzzling is Nolan's remark that he does not recall there being any kind of writing on the envelope when he initialed it. If true, it means that the information about the content was added later and thus could differ from the real content.