On Special:ipblocklist, I see three basic types of entries. I
only understand two of them.
First, there's the ip block, for example:
'Joe Sysop blocked 123.123.123.123'
Second, there's the username block:
'Jane Sysop blocked ReallyOffensiveName'
Third, there's these:
'Joe Sysob blocked #1521'
What are those? There's no link to the contribs, so it's impossible
to see what they are. The number appears to be the number of the block,
not an identifier of what was blocked.