First, I think it's important to note that actual legal liability is going to vary case-by-case, it's never so simple as "They were the engineer, it's their fault." In situations where something happens and lawsuits are drawn up, they're probably going to name every single company who is at all related, and all key people in those companies responsible for the design. However, I think I can give some general insight based on my experiences and what I've been told in legal liability training.
Personally, I lay the majority of the blame in this situation on the owner, who uses plans that are years old without having anyone qualified look at them and update them. I've seen (small) issues with this in my position. Drawings are completed and sent to another department for approval, and for whatever reason, they sit on an application engineer's desk for months, sometimes close to or upwards of a year. The drawings are then sent out as-is, but internal changes that have been made to drawing standards since the drawings were originally updated aren't complied with. These are minor issues, but it's easy to see this occurring on a larger time scale and with more serious consequences.
The drawings should be dated. That's fairly common practice, and this is one good reason why. We want to know when the drawings were made, to determine what things have changed since that design, whether that be standards, codes, laws, or simply interfacing parts. If the drawings are made to the codes and standards in place at that time, I don't see how the engineer can be held responsible for that design, unless it can be shown that the engineer had knowledge of the code needing a revision for safety issues. In this case, making the print fit the code isn't good enough, because we know the code won't prevent some issues.
It really comes down to the fact that, in the design process, every consideration towards safety needs to be taken, and where risk cannot be eliminated, it needs to be made clear what the risk is and how it can be mitigated by the end-user.
On the second point, this sounds like a very gray area, and I really couldn't discuss any legal aspects of this. But I will say that I think, if an engineer knows that the design being built is out-of-date and could cause issues in some manner, they have an ethical responsibility to contact someone still affiliated with the project and apprise them of the situation. It may not be their legal responsibility, but I think it's clearly the right thing to do.
It should almost go without saying that any engineer still affiliated with the project has the same obligation, only stronger, to say that the designs need to be updated and they cannot be used in their current form.
To give some context for this, the main product that my company manufactures can be extremely dangerous in its operating environment. Guarding is absolutely required unless the product is entirely shielded by other parts of the machine. The guarding itself may vary slightly from company to company, but its largely the same because it's governed by an ISO standard. However, this standard has changed over the years, and even the organization that creates the primary standard has changed. This means that we have old designs which feature old guarding that are still active in our system. We have one employee who is extremely knowledgeable about the industry and in particular the safety codes and even sits on some safety committees. He makes sure that new designs comply with the guarding standards and that old products are updated as necessary. Sometimes this means going so far as to tell the customer that we won't sell them this product if they won't let us update the guarding (newer guarding is in some cases more expensive). He isn't always the most popular person, but this is his job, and that's how we manage our code compliance in a world where codes and standards are not consistent.