Russell,
The 10cm core removal is standard now and should be supplied like that.
It is worth checking if you are having difficulty with the knot passing the fairlead. If the core is there it is easy to pull out 10cm and cut.
When you tie the two together it is important to tie the 'hollow' end of the fat part to the thin part, thereby making a smaller knot.
It had been noticed that the 10cm core removal is not described in the rigging guide on page 17 and I know there is already a re-draft done by RS of that page with it in.
The double sheet bend not being accurate has also been picked up already and the page awaits another re-draft. It is the busy season now so that action will be down the RS priority list for now.
Here is a Double Sheet Bend;