... if something else is not ... Otherwise it will grab ... no?

Why not try it and see?

>perl -wMstrict -le
"while (<>) {
   chomp(my $acc = $_);
   my $ternary =
     ($acc =~ /(^USA|^BRA|^CAN)?(.*?)(IN)?$/i) ? $2 : $acc;
   my $capture2 = defined($2) ? $2 : 'undefined';
   print qq{input: '$acc'};
   print qq{ternary: '$ternary'  \\2: '$capture2'};
   }
"
USA1111
input: 'USA1111'
ternary: '1111'  \2: '1111'
BRA1111
input: 'BRA1111'
ternary: '1111'  \2: '1111'
xxxUSA1111
input: 'xxxUSA1111'
ternary: 'xxxUSA1111'  \2: 'xxxUSA1111'
foo
input: 'foo'
ternary: 'foo'  \2: 'foo'
^Z
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