Label last page in sequence of includepdf commands

I am in a tricky situation. I am using NewEnviron to separate a handful of major parts of my document. Each part has its own numbering scheme and several environment-specific commands and settings. Important for my question, all numbering schemes follow the principle page_current of page_total

If I now, however, insert pdf-documents using includepdf, the label for page_total breaks if includepdf is executed on the last page of my document.

Here an mwe, which probably explains it a bit better.

documentclass[fontsize=10pt]{scrartcl}

usepackage[T1]{fontenc}
usepackage[utf8]{inputenc}
usepackage{mwe}

usepackage{pdfpages}
usepackage{environ}
usepackage{scrlayer-scrpage}

NewEnviron{myenvi}{%
    clearscrheadfoot%
    cfoot{normalfontthepage / pageref{lastpage}}%
    clearpage%
    BODY%
    label{lastpage}%
}

newcommand{myincludepdf}[1]{includepdf[scale=0.5, frame, pagecommand={}]{#1}}
%newcommand{myincludepdf}[1]{includepdf[scale=0.5, frame, pagecommand={label{lastpage}}]{#1}}

begin{document}

    begin{myenvi}
        lipsum[1-15]
        myincludepdf{example-image-a4}
    end{myenvi}

end{document}

I also tried to add my label to the post-code of includepdf. That doesn’t help.

I found two ways to get it to work. But both are not satisfactory. The first one is simply to add another page to the document. Because then the label{lastpage} can execute again. Moreover, one can also add the label{lastpage} to the pagecommand-option of includepdf. But then I get a lot of “lastpage multiply defined” warnings.

Anyone an idea how to solve this issue. I was considering using a counter or gdef or something. But I think it is not really possible to get around this problem without the help of a sidecar-file.

Is there maybe an option to directly manipulate the aux-file so that I don’t produce multiple labels and only the last call of label{lastpage} remains?

documentclass{scrartcl}

usepackage[T1]{fontenc}
usepackage[utf8]{inputenc}
usepackage{mwe}

usepackage{pdfpages}
usepackage{environ}
usepackage{lastpage}
usepackage{xifthen}
usepackage{scrlayer-scrpage}


NewEnviron{myenvi}{%
    clearscrheadfoot%
    cfoot{normalfontthepage / pageref{endenvi}}%
    clearpage%
    BODY%
    label{endenvi}
}


newcommand{myincludepdf}[1]{includepdf[scale=0.5, frame, pagecommand={%
        ifthenelse{equal{pageref{LastPage}}{thepage}}{label{endenvi}}{}}]{#1}}

begin{document}

    begin{myenvi}
        lipsum[1-15]
        myincludepdf{example-image-a4}
        myincludepdf{example-image-a4}
    end{myenvi}

end{document}