angst, this is what I've got...
12A - game + a + yob = end of clue (think footy), with 2 extra letters added
19A - irrationality is def'n; uniform (think phonetic alphabet) + when inside an artistic type of light, with 1 extra letter
20A - make is def'n; issue + Roman 50, with 1 extra letter
9D - I don't get it either! (I have an answer)
21A - not sure if this is an extra letter one or not, as I didn't add them up. Works both ways. First part of clue gives you a name, which is made up of typically + American
26A - first part is def'n = a + trim
Hope this helps.