In my experience pretty much at all levels of design skill the work gets passed to an engineer at some point in the process. Either an in house engineer or a outside engineer at the factory. Also if you are making products in Asia they will a lot of times rebuild any model sent to them to better integrate with there systems. Generally I would say there are usually a number of check points along the road for people with specific experience with making the parts to way in and add there perspective. So I would agree with the above comments that what is important is basic understanding of molding plastic not so much a complete formal understanding. Such terms as undercut, draft angle and knit line are terms you should recognize but how to deal with all the problems and there solutions might not necessarily be expected. Same would hold true for plastic properties there is a lot of them and that more then likely would not be expected of you to know. But you should be familiar with the families of plastics such as LDPE, HDPE, PP and so forth and so on.