So recently I got a few spambots on my wiki, which prompted me to install CU. There were five accounts in total, they made spam pages and/or spam userpages. I blocked all five indefinitely, deleted their pages, and hid their usernames (On a side note I am now the only one who can see those usernames in the BlockList, for others the list is empty) I decided to install CU to try and get an IP range, and they're all returning "no matches found". The extension is certainly working because I tested it on myself and got my own IP address, so why did these accounts seemingly have no IP at all? A final note I should add is that after installing the extension, all the Autoblock entries on the BlockList disappeared, though the accounts names were still there.
Topic on Extension talk:CheckUser
It may not be able to get that info if you installed the extension after those edits were made.
Ah that might be the reason. Well then it should probably work if any more spambots show up, the offending accounts are blocked, that's what matters.