Giove, it may just have been FR'ed in India. RFI is not listed as ever using Z as a prefix/suffix. There is great variability in the positioning of the letters in serial numbers; most serials are letter prefixed, but some suffixed.......
AFAIK the letter associated with a number is there just to distinguish the different blocks of numbers; 'A block', 'B block' etc., & the positioning before or after doesn't have any deeper significance, although the majority of letters are before the digits.