Hey, Gaz,
I did take a look at my own example but, even under the loupe this morning, I couldn’t confirm the number of strings on mine, due to strike weakness.
There is this post…
…where Rob’s and Jelida’s examples show 5 strings. I did notice however that Coys’ Penny, shown in the same thread, displays a harp with six strings. I can’t imagine that the 1d harp punch hasn’t at some point been shared across the denominations?