prince-trim and prince-bleed seem to be acting differently in Prince 9, at least compared to Prince 7.
For example, with the following CSS:
marks: crop cross;
In both cases the PDF will extend 30 + 15 = 45pt beyond the page boundary. But in Prince 7 the crop marks do not extend into the bleed area, and so are 15pt in length. In Prince 9, the crop marks extend to within 6pt of the page boundary, and so are 39pt long. Prince 7's behaviour in this case was acceptable to our printers, but the Prince 9 behaviour is not.
Most of the large commercial printers we work with do not want the crop marks to extend into the bleed area. A common setting is to have the "marks offset," which is the distance from the page boundary to the crop mark, to be 30pt while the bleed is only 13.5pt. This property is adjustable in most page layout programs like InDesign or Quark.
We need to be able to control the marks offset, as the required value ranges from 9pt to 30pt in our experience. So I'd prefer that the bleed amount not influence the placement of the crop marks. The mark offset would become a property, which in conjunction with bleed and trim would give us a lot of flexibility.