Arabs and a number of other middle eastern people use the RTL (right to left) style so maybe 532 52 on the etchings. I learned the markings for 18K (١٨) or 21K (٢١) gold in the early 80's on a military exercise to Egypt.
Ok... I said maybe.No. Arabic words are written and read as RTL (right-to-left), but numerals (including dates expressed as numerals) are written and read as LTR (left-to-right) as we would in English.
That agrees with what you learned about gold purity marking...'١٨' is '18' and '٢١' is '21' (both written and read as LTR)