With chagrin, I must admit that I was thinking syntax, and testing proves me wrong on that account.

However, grashoper is not looking for '{IND' but, rather, for "3 letter account codes...."

If I understand that correctly, the condition in the regex in Re^2: regex testing for multiple values

if ($Session->{'usrSystem'}=~/{IND|NOR|PRO|ARM|SND/s)

introduces an open_curly_brace ({), which is wrong, in part, because the regex then tries first to match on for an open_curly_brace.