u/Mammoth-Emergency623

I recently saw this painting MOMA and I’m a bit confused about the title.

Why does it have a dual number like "No. 5 / No. 22"? I see some of his other works are just like No 6 or No 7, but how could this piece be both 5 and 22?

Would appreciate any insight into how to interpret or understand these titles in the context of his broader work. Thank you so much in advance!!