DO NOT take first 3 characters from a month name to get an abbreviated month name. This can give you duplicate results in some languages as first 3 characters of two months may be same.
I have encountered this with the Czech language.

So, use the following:

If the month is 1 i.e. January

So, to get abbreviated month name ALWAYS use

Monthname(1, True)

This will always return standard abbreviated month name.