Credit report - what do "entry code" & "source" mean?

LittleWing294

Reading my credit report, I see that every item has an "entry code". I can't find an explanation of what these mean, and I'd like to know out of curiosity if nothing else. Can anyone point me to an explanation of them?
I'm also trying to work out "source".
The entry that got me curious, this month, was the addition of a new linked address for me. It's a valid linked address, but one I moved from many years ago. The "source" shows as O2 - is that the telecom company, or a code? (If the telecom company, I had a phone with them years ago, but not currently) The "entry code" shows as B1.
Any clues to understanding these would be welcome!

[Deleted User]

The entry code is to identify the account in question on your report when you raise a query with the CRA

Halfie

The Source is who told them about the change. For example, I changed addresses and the source is listed as my bank. For another address change it lists the source as a mail order company.

D_M_E

Linked address and source O2 - I'd be getting on to O2 and telling them a suspected fraud is in progress as you moved away from that address years ago and don't currently have an O2 account nor have applied for one recently.

Either that or they have resurrected your old account - which you did close and fully paid up, yes? - and you could be getting debt collectors chasing for an alleged debt.

[Deleted User]

As above ^^^^ get onto O2 and require an explanation.

LittleWing294

Thought I'd give a quick update on this, many months later. At the time (last July) I spoke to O2, they did some searches but couldn't find any reason why anything should be appearing right then.
The entry stayed on my credit report until last month, when it disappeared. I'm none the wiser.
I've decided it's a puzzle but hopefully nothing more serious.