We do something similar, using a 3-letter code for the hymbook, eg:
TIS675 = Together in Song #675
CAH023 = Complete Anglican Hymns #23
This way they group within the hymn books. We also use separate Dropbox folders for each hymn book for backup.
We are also using Songs for Liturgy elements because we felt Custom Slides don't have sufficient formatting options. So for these we use a Lit code, eg:
Lit_01_Gathering_Lent refers to a short "chunk" of liturgy for which the season of Lent will have a different version than say the season of Easter. This means all our Lit chunks group together, also we can easily see all the different Lit_01 variations adjacent to one another.
We also use Songs for psalm "chunks". Each Sunday of the 3-year RCL cycle will have its own psalm. I am using a numbering system for the Sundays in the 3-year cycle, eg. coming Sunday is 022B (4th Sunday of Lent, Year B). So the title for the congregational psalm for this week is:
Psalm 107.1-3, 17-22 (022B)
Again, all the Psalm lections will group together and the user can easily see which one to select.
All this does make for a very full Songs folder! But it is easy to navigate and to back up different sections separately. As a suggestion to the devs it would be great to have a series of horizontal tabs within the same category so they would display side by side.