... is how your responses are bounced from one person to another.
In my case, I've never had a second letter from the same Sender.
(As you can see from my letters) In the first instance they used
Reference Number: "301653"
Which morphed (by some strange magic) into: "LIT.10.2/0001784"
Which then re-morphed (by even more magic) into: "1813492"
Which indicates the "bouncing".
The pen is mightier than the sword, folks.