Why is the letter Dhal not on the arabic keyboard stickers

I got arabic keyboard stickers but the letter dhal was missing. And after looking it up online (https://www.google.nl/search?q=arabic+keyboard+stickers&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj6xYaCspvVAhWBBBoKHbM2DjQQ_AUICygC&biw=1440&bih=709#imgrc=jF2p1p5TfH7GpM:) no sticker set got the Dhal on the sticker.

But my macbook does has Dhal it under the backslash key.

Anyone knows why this is?