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/\x26\x67(?!\x26\x67)(.(?!\x26\x67)){6}.{2}/s

 perl -le 'print for map { /ab(?!ab)(.(?!ab)){2}.{2}/s ? $& : () } @AR
+GV' abhjabdf abasdasd abdasdadsab ababblah
OUTPUTS:
abasda
abdasd
abblah

  /
    \x26\x67     # Starting sequence (let's call it AB)
...
                 # note we know they're not AB because otherwise the
                 # (N-2)th item in the previous part wouldn't have mat
+ched
  /sx            # Enable comments, and make . mean everything

  my $marker = '&g';
  my $N = 8;
  my $n1 = $N-2;
  /$marker(?!$marker)(?:.(?!$marker)){$n1}.{2}/s