I read that as meaning “four more examples” to those found in the letters extracted from the clues so that there are 8 representations in total. 4 in the clues and 4 in the grid.
I too spent rather long looking for a fifth representation in the grid before realising what was required. Candledave's post above explains it beautifully, and far more succinctly than I ever could.
I’ve completed the grid and identified the thematic representations in 4 rows. However, I’m baffled by how to extract the letters from the extra words or what they have in common. Any nudges greatly appreciated.