I think you don't need to consider shrinkage factor. You should know you are responsible for product design such as construction of end parts in assembly. For manufacturing issue, moulding of plastic part should be taken care by tool maker. They receive your end product with required part for moulding. Their task is to design tooling for each different part. Shinkage factor is the one they consider in tooling design
I hope it's clear to you in product design process. Of course you understand better tooling process is benefitial to your work in product design. At least you won't design part that have undercut or too weak to be ejected from the tool