Ron has found that

One can make a considerable error by not starting a pc out on Dianetics with a C/S-1 on the basis that the pc has already had lots of Scientology auditing.

That a pc has had lots of Scientology auditing is no guarantee that the pc understands such things as erasure or what a Dianetic session or even what auditing is all about.

The C/S-1 must be well done. If not you will have a pc not running well because he didn't know the terms or what was expected in session.

A C/S-1 can be done again if the pc doesn't do well on Dianetic C/S-2.