Note that there are no propers in this collection for Good Friday. The reason for this, of course, is that there is no Introit, Offertory or Communion prescribed for this day. The SEP collection is only focusing on these three processional chants, which are typically the bulk of the proper for typical Sundays and Feasts, but as we know, Holy Week is its own beast.
One place where I broke the convention of the book was with the Offertory that is prescribed for Holy Thursday in the Graduale Romanum. This is the well known and very simple Ubi Caritas. The text and the musical setting for this chant are verbatim from the new English translation of the Roman Missal. The musical structure is identical to the Graduale Romanum and the text is newly translated as a part of the Roman Missal effort. I actually find it to be very nice!
So while the Simple English Propers book will be very useful for the week-to-week liturgical “grind”, when it comes to Holy Week additional resources will surely be needed.