I have a xml structure like this:

<nc>
    <mod>
        <grp id="d0e9f2f84">
            <des>GROUP_33</des>
            <num>--33</num>
            <seq>33</seq>
            <des2>GROUP_33</des2>
            <art>
                <num>15-33-101-00678</num>
            </art>
        </grp>
        <art>
            <num>15-36-072-00000</num>
        </art>
        <art>
            <num>13-42-099-30002</num>
        </art>
        <art>
            <num>15-42-001-45331</num>
        </art>
    </mod>
    <mod>
        <grp id="d0e9f2f84">
            <des>GROUP_33</des>
            <num>--33</num>
            <seq>33</seq>
            <des2>GROUP_33</des2>
            <art>
                <num>35-33-101-40678</num>
            </art>
        </grp>
        <art>
            <num>11-42-045-41002</num>
        </art>
        <art>
            <num>12-42-101-46331</num>
        </art>
    </mod>
</nc>

Normally the correct structure is /nc/mod/grp/art but sometimes i have articles (art) that are orphans such as /nc/mod/art.
I am trying to automatise the following. When i have orphan articles, insert a node group (grp) and depending on the second sequence of the articles number (num) for example ([0-9]{2}-42) insert a grp node.

My try with this code snipet:

let $input:=doc("file:/C:/Users/FOB/Documents/git_documentation/private/test_mod_art.xml")
    return
        for $ii in $input//mod/art[not(ancestor::grp)] return 
        if ($ii[matches(num, '^[0-5][0-9]-36')]) then
        
        insert node <grp id="d0e1f2f21"><des>GROUP_36</des><num>--36</num><seq>36</seq><des2>GROUP_36</des2></grp> before $ii
        
        else if ($ii[matches(num, '^[0-5][0-9]-42')]) then
        
        insert node <grp id="d0e1f2f23"><des>GROUP_42</des><num>--42</num><seq>42</seq><des2>GROUP_42</des2></grp> before $ii        
        else
        ()

It works, but this code doesn’t take into account the fact, that sometimes we have more than one node who matches ‘^[0-5][0-9]-42’, for example.
So i need to detect those and group it before insertion of a group node. I have read some articles with the function distinct-values (at the moment my saxon processor doesn’t accept the group by clause), tried some code, but unfortunately I don’t have enough knowledge to be able to understand it.
How can i achieve this, could some friendly souls give a try specially so that I can understand?

Thank you!

Expected result:

<nc>
    <mod>
        <grp id="d0e9f2f84">
            <des>GROUP_33</des>
            <num>--33</num>
            <seq>33</seq>
            <des2>GROUP_33</des2>
            <art>
                <num>15-33-101-00678</num>
            </art>
        </grp>
        <grp id="d0e9f2f85">
            <des>GROUP_36</des>
            <num>--36</num>
            <seq>36</seq>
            <des2>GROUP_36</des2>
        </grp>
        <art>
            <num>15-36-072-00000</num>
        </art>
        <grp id="d0e9f2f33">
            <des>GROUP_42</des>
            <num>--42</num>
            <seq>42</seq>
            <des2>GROUP_42</des2>
        </grp>
        <art>
            <num>13-42-099-30002</num>
        </art>
        <art>
            <num>15-42-001-45331</num>
        </art>
    </mod>