Hi!
On wikipedia (
https://en.wikipedia.org/wiki/Bengali_numerals) there is this picture of Bengali numbers:
On numista page for this coin there is for particular year on comments also written western year (Arabic numerals) with Bengali numerals:

Here one can see how it looks year 2005, 2006 and 2008 written with Bengali numerals.
On picture where is written difference between versions km #26.1, km #26.2 and km #26.3 one can see that those writings don't match:

I'd say the first coin is year 2006, second 2008, third 1996 (and different coin, that one is KM #18.3).
Borut