You can get it by putting in
Sc* (Phonetically similar variations)
Annie
Amelia
1864
Well that shows how much attention I pay. When did they start allowing wildcards?
I don't believe the GRO have started supporting wildcards.
I think what you're seeing here is just a result of the algorithm the GRO are using for phonetic matching (Metaphone) and how they're using it. They're matching on any name where the Metaphone code is the same or has up to one character different.
For the names
Sc,
Sc* and
Sca* the Metaphone code is
SK. For the name
Sean the Metaphone code is
SN. As these are just one character different the GRO are treating this as a match.
Here's a useful page if you want to check what the Metaphone code is for a given name:
Metaphone Calculator for Genealogy Searches by Ancestor Search
http://www.searchforancestors.com/utility/metaphone.phpAs for wildcard matching, they have built support for it but for some reason they've disabled it in the UI. It's quite trivial to enable it, and it does work, but it's almost certainly against their terms-of-use to do so.