This may have some idea where to start, or then again it might not :)

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11163097
use warnings;
use List::Util qw( reduce );

local $/ = ''; # read paragraphs
while( <DATA> )
  {
  my @terms = /<term>(.*?)</g;
  print "Input: @terms\n";
  my @fails;
  reduce {
    if( $a =~ /^\d/ )
      {
      $a + 1 == $b or push @fails, "fail at $a -> $b\n";
      }
    else
      {
      my $left = $a =~ tr/a-z/b-za/r =~ s/^a/aa/r;
      $left eq $b or push @fails, "fail at $a -> $b\n";
      }
    $b } @terms;
  print @fails;
  print "\n";
  }

__DATA__
<list>
  <item>
    <term>1.</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
  <item>
    <term>3.</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
  <item>
    <term>4.</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
</list>

<list>
  <item>
    <term>a)</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
  <item>
    <term>b)</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
  <item>
   <term>d)</term>
   <para>jhjhjh hjkjkjkj</para>
  </item>
</list>

<list>
  <item>
    <term>aa)</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
  <item>
    <term>cc)</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
  <item>
    <term>dd)</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
</list>

<list>
  <item>
    <term>xx)</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
  <item>
    <term>yy)</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
  <item>
    <term>zz)</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
  <item>
    <term>aaa)</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
  <item>
    <term>bbb)</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
  <item>
    <term>yyy)</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
  <item>
    <term>zzz)</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
  <item>
    <term>aaa)</term>
    <para>jhjhjh hjkjkjkj</para>
  </item>
</list>
[download]

Outputs:

Input: 1. 3. 4.
fail at 1. -> 3.

Input: a) b) d)
fail at b) -> d)

Input: aa) cc) dd)
fail at aa) -> cc)

Input: xx) yy) zz) aaa) bbb) yyy) zzz) aaa)
fail at bbb) -> yyy)
fail at zzz) -> aaa)
[download]

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