BM674.4-59 is used when the "Mahazor" encompasses the liturgy for various
festivals collectively.
The uniform title for the text would be Mahzor (possibly qualified
by rite, movement, etc., but without a subsequent $p for a particular festival
or named group of festivals).
This class number replaced BM675.F45.
BM675.P59 is for Mahzor. Pilgrim Festivals (encompassing only Shalosh
Regalim)
BM675.R67 is for Mahzor. Rosh ha-Shanah (only)
BM675.Y58 is for Mahzor. Yom Kippur (only)
Note: There is also BM675.H5 for Mahzor. High Holidays (Rosh ha-Shanah and Yom Kippur together)
Lenore