It might me easy to add and drop at contract but this has an affect on your build later on. For example say you wanted an external tap at one location. On Contract drawing that you found it is on the wrong location. You tell the CSC to change the location on contract and on the drawings before you sign it. She would says PD will not allow you to change the drawings or contract to the correct location before signing the contract. So you sign the contract knowing it is on the wrong location. The CSC will tell you don't worry we can change it as post contract variation. A Week before you build you will get your final drawing and the tap will be on the correct location. When the build start the tap will be installed as per oringal contract drawing (wrong location). It is ok for them is it our bricks that has to come down to fix the issue. PD might want to seriously think about when to send the drawings to their trades people. Only send it once the drawings have been signed by the customer a week before the build otherwise there are unwanted issues hanging around. Wrong things are getting installed. Things would get fixed in the end but don't want to pull the plaster down or bricks down to fix the mistakes the admin department makes.
Well said Yellow,
& it helps a lot if the SS does something straight away to fix whatever defects there are before further work is done.