I've conjured up a nice short solution for you. It breaks the appropriate columns into chunks based on alpha- or numeric-ness and then compares them.

#! /usr/bin/perl
use strict;

while (my $line = <DATA>) {
  chomp $line;
  my @line = split ";", $line;
  next if $line[0] eq $line[1];
  next unless length $line[0] == length $line[1];
  my @one = breakup($line[0]);
  my @two = breakup($line[1]);
  next unless scalar(@one) == scalar(@two);
  my @match = map { $one[$_] eq ++$two[$_] ||
                    ++$one[$_] eq --$two[$_] ? 1 : 0 } (0..$#one);
  print $line, "\n" if 1 == grep {$_} @match;
}

sub breakup {
  my @out;
  while ($_[0]) { $_[0] =~ s/^([a-zA-z]|[0-9]+)//; push @out, $1; }
  return @out;
}

__DATA__
VIR19;VIR20;VIR;B744;
VIR19;VIR207;VIR;B744;
VIR19;VIR21;VIR;B744;
VIR19;AF34B;VIR;B744;
VIR19;AF34C;VIR;B744;
VIR19;IB580F;VIR;B744;
VIR19;IB581F;VIR;B744;
VIR19;AL34BC;VIR;B744;
VIR19;AL34AC;VIR;B744;
VIR19;ADH00A;VIR;B744;
VIR19;ADH01A;VIR;B744;
AL34BC;IB580F;VIR;B744;
AL34BC;IB581F;VIR;B744;
AL34BC;AL34BC;VIR;B744;
AL34BC;AL34AC;VIR;B744;
AL34BC;ADH00A;VIR;B744;
AL34BC;ADH01A;VIR;B744;
[download]

Prints:

VIR19;VIR20;VIR;B744;
AL34BC;AL34AC;VIR;B744;
[download]