While  Haggadah and other liturgical headings are not included in the list of valid free-floaters for sacred works (SCM
H 1188), LC has applied subdivisions valid for literary works (SCM H 1155.8).  Therefore "Haggadah--Adaptations" and
"Mahzor--Adaptations" are valid but not "Haggadah--Commentaries."

It is always a challenge to deal with these "non-standard" liturgical works--how to apply uniform titles, subject headings, classification, etc. How different must something be to be considered non-standard? The matter has come up on various occasions at Hebraica Team meetings.

As far as subject assignment, Hebraica Team members have, in general, refrained from using the standard array
"[         ]--Liturgy--Texts" headings for these "non-standard" works, and instead have applied the subdivision
"--Prayer-books and devotions."
Please be aware, however, that "Jews--Prayer-books and devotions" is a reference to "Judaism--Prayer-books and devotions"
and that the subdivision is further subdivided by language.  Also, it may be assigned after topics.

So, LC suggests the following array of headings:

[Uniform title]--Adaptations.
[Holiday]--Prayer-books and devotions--[Language].
Judaism--[Place]--Prayer-books and devotions--[Language].
[Additional topical headings]

The other problem is classification.  A special subarrangement was established for "miscellaneous adaptations" of Haggadot (BM674.795), but not for Siddurim or Mahzorim.