P6 has dates that are called External Dates. Do you know that they are a constraint, they may significantly change your program and may be created without you knowing?

External Dates can be career shortening if you do not know how they are created, how to find them, delete them or turn them off!

If you wish to understand about External Dates then look at this paper with is an extract from my Planning and Control Using Oracle Primavera P6 PPM book by clicking on this link>>>.