Late as usual I see...
Here is my suggestion 
#!/usr/bin/perl
use strict;

{
local %_;
    while(<DATA>){
        chomp;
        if(/(\d+|[A-Z])$/){
            $_{substr($_,0,(length($_)-length($1)))}->{$1} = $_;
        }
    }
    for(sort keys %_){
        if(scalar(keys %{$_{$_}}) % 2 == 0){
            local @_ = sort{$a <=> $b || ord($a) <=> ord($b)}keys %{$_
+{$_}};
            for(my $i = 0; $i < scalar(@_); $i+=2){
                if( ($_[$i] =~ /\d$/ && abs($_[$i] - $_[$i+1]) == 1) |
+| (abs(ord($_[$i]) - ord($_[$i+1])) == 1) ){
                    print $_{$_}->{$_[$i]}.";".$_{$_}->{$_[$i+1]}."\n"
+ ;
                    print $_{$_}->{$_[$i+1]}.";".$_{$_}->{$_[$i]}."\n"
+ ;
                }
            }
        }
    }
}
__DATA__
AAA30
BBC5
SHT12H
DAL33B
BBC49
AAA31
BBC8
BBC3
DAL33A
BBC6
SHT12G
BBC50

[download]
Output 
AAA30;AAA31
AAA31;AAA30
BBC49;BBC50
BBC50;BBC49
DAL33A;DAL33B
DAL33B;DAL33A
SHT12G;SHT12H
SHT12H;SHT12G

[download]
Not exactly the OP's output but close...
Just a thought :)

-InjunJoel
"I do not feel obliged to believe that the same God who endowed us with sense, reason and intellect has intended us to forego their use." -Galileo

In reply to Re: searching for strings by injunjoel
in thread searching for strings by steph_bow

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