=MATCH(AB2,{"A","B","C","D","E","F","G","U"},0)

What do the curly braces do in this formula? (Stupid question I'm sure, but I'm not familiar with them). Also, and link (for beginners) to how special characters are used in Excel would be appreciated.

{"A","B","C","D","E","F","G","U"}

is a 1-column table. Also called a vector.

It's equivalent of having a range housing the same values: for eaxample, A2:A9 filled with A, B, C,.. respectively.

=MATCH(AB2,{"A","B","C","D","E","F","G","U"},0)

would then become:

=MATCH(AB2,$A$2:$A$9,0)

BTW, the formula omits your A* for it would be confused with A. If that's still relevant, try to clarify what values with A* are meant. If literal A*, modify the formula as Sunnyland suggests to:

=MATCH(AB2,{"A*","A","B","C","D","E","F","G","U"},0)-1