Distinguishing between two North Yemen 1 rial notes

Does anyone know how to tell these two North Yemen notes apart?

It looks like P11a can be distinguished by the signature, but P11b and P16b seem to have the same signature and as far as I can tell, look identical. The printers are apparently different but I don't see any printers' marks on the notes.

N#208791

N#210759

Hello 🤖

Without pictures, it will be very difficult for anyone to help you. Could you please post clear pictures of each side of your item?

Please note that this is an automatic message. Feel free to ignore if it is not relevant.

You have raised an interesting question. It looks like one is printed with a much stronger underprint than the other, and according to this site, these were printed by two different imprinters, and were issued separately.

If I had both notes, I would not know that they are not the same.

P/s… just cheeked, and in fact I do have the nd1983 print, or was it?

Hi

I have both notes

P-16B has clearer underprint design (more than P-11b)

I found:

P-11b has prefixes i/1 - i/43

P-16B has prefixes i/49 and higher including next letter ب