This box has historically definitely always been ignored. There seems to be a glitch - I wrote “please could I have a black t-shirt” in this box when I placed my first ever order. They didn’t read it and sent me a grey t-shirt.
Since then I’ve never filled in this field again, and it appears blank when I place an order, but on every single order confirmation that comes through, the original t-shirt message is repeated. I think this is why they ignore it. Because old messages never get removed.
This may have all been cleaned up tho with the new interface. We shall have to test it and report back!!
I used to have a job where I had to interact with a uk wide service provider and they never acknowldedged the special instructions box. In the end i used to write all sorts of random rubbish because it was so pointless and frustrating…