Position of addendum field with regard to the related field

The field addendum is supposed to be displayed at the very end of a bibliography entry. But in the case in which that item contains a related string, this is not true anymore. Is there any other field one could use instead of addendum?

documentclass{article}
usepackage[authordate,backend=biber,indexing=true]{biblatex-chicago}
addbibresource{jobname.bib}

begin{filecontents*}{jobname.bib}
@misc{RauSūSaṃ,
entrysubtype = {classical},
title = {Rauravasūtrasaṃgraha},
addendum = {Also consulted: Mysore ORI MS B~776.},
related = {Bhatt1961},
relatedoptions = {useeditor=false,usetranslator=false,skipbib=true},
}

@book{Bhatt1961,
editor = {N. R. Bhatt},
title = {Rauravāgama},
volume = {1},
series = {Publications de l'Institut Français d'Indologie},
number = {18.1},
publisher = {IFP},
location = {Pondicherry},
year = {1961},
}
end{filecontents*}
begin{document}
nocite{*}
printbibliography
end{document}

EDIT:

As as clarification: The relationship is one of primary and secondary bibliography, more or less as here. Thus the two entries would normally be displayed in two separate bibliographies, which I left out from the example above, to keep it simple.

In theory, a beautiful solution might be to have the addendum be displayed after the related information only for entrysubtype = {classical}. Anyway, I can also work with the current behaviour, copying Bhatt1961 to a new entry which gets only sourced by the respective primary bibliography entry, and adding the addendum field there. Not quite ideal, but as these cases are rare it wouldn’t be too much of a problem.

EDIT:

I now realize that I do have quite a number of entries of this kind, pertaining to different papers in the same book, all of them having their own bibliographies, so a cleaner solution would be great. I’ve thought of using the fullcite command in the note field for the main reference, and the addendum for "Also consulted.":

documentclass{article}
usepackage[authordate,backend=biber,indexing=true]{biblatex-chicago}
addbibresource{jobname.bib}

begin{filecontents*}{jobname.bib}
@misc{RauSūSaṃ,
entrysubtype = {classical},
title = {Rauravasūtrasaṃgraha},
addendum = {Also consulted: Mysore ORI MS B~776.},
note = {fullcite{Bhatt1961}},
}

begin{filecontents*}{jobname.bib}
@misc{RauSūSaṃ2,
entrysubtype = {classical},
title = {Rauravasūtrasaṃgraha},
addendum = {Also consulted: Mysore ORI MS B~776.},
related = {Bhatt1961}, 
relatedoptions = {useeditor=false,usetranslator=false,skipbib=true},
}

@book{Bhatt1961,
editor = {N. R. Bhatt},
title = {Rauravāgama},
volume = {1},
series = {Publications de l'Institut Français d'Indologie},
number = {18.1}, 
publisher = {IFP},
location = {Pondicherry},
year = {1961},
}
end{filecontents*}
begin{document}
nocite{*}
printbibliography
end{document}

which almost works, except for two points:

1. I would need another command instead of fullcite, one which keeps the year at the end. Would it be possible to call whichever internal command takes care of the regular formatting of the entry, such as in the third entry, i.e. RauSūSaṃ2, with the year at the end instead of after the editor?

2. I would want to exclude Bhatt1961 from the bibliography. Unless it gets cited in the paper of course. If it was done via related entry that would have been done by skipbib=true as one of the relatedoptions. Here I would probably want to do something like in the third approach in this answer. I would have to check it manually, but that’s okay.

Alternatively, is there any field one could use as the very final field to be displayed, even after related? Or, how would I define such a field? Or, how would I change the order of display of related and addendum?