surely that's the reason police are not supposed to change the numbers ? so not to open themselves to possible suspicion?
There is no rule against changing exhibit numbers if you later learn that someone else was the person who found the items in fact that is preferable because the whole point of the system is so that from the prefix you can know who found the item.
However if you do that then you have to go through all the documents in the case to make them match up so there is no confusion. Whiddon did exactly that and there was no confusion. After the trial the defense found out about the changes. Jeremy crafted wild conspiracies to COLP crafted around such but they all were found by COLP to be complete nonsense.
For instance alleging that David Bird found a silencer on the day of the murders, that this moderator was marked DB/1 on that day and he took such moderator into custody.
COLP determined that David Bird assigned DB/1 to a photo. David Bird didn't collect physical evidence he took photos at the scene. The first reference to a moderator being marked DB/1 was when all 4 items found by Boutflour were changed to the DB prefix. Proof existed that DB/1was in use for a different exhibit well before a moderator was referred to as DB/1.
Since there already was a DB/1-4 and in fact much more it was easier to change the 4 items to DRB then to have Bird change his hundreds of exhibits to something else. It is beyond question that they could not leave the items DB/1-4 given there already was such an exhibit. They would have to change either the 4 exhibits again or change Bird's exhibits. So it is sheer folly to try alleging anything around the second chance to DRB. Yet some do exactly that but do so inconsistently. Though the scope went through 3 changes they don't allege there were 3 scopes. They just allege 3 moderators.
Given COLP's findings it is a waste of time to try pursuing this line but some don't care and are out to use anything they can no matter how ill advisable it might be. Legal minds look for something legitimate while propagandists look for anything they can try to fool people with