How are the lawyers (or the lawyer firm) able to prove it was never opened? Do they enlist a forensic expert?
Well I don't really want to hijack this thread, but I'll just say that it's generally not the defendant's job to "prove" anything in a copyright infringement suit.. they merely need some sort of defense that shows that it was more likely than not that they, in fact, did not use the materials that were sent to them. A defined and long-held corporate policy along with witnesses and records tends to do that.
It's very difficult to "prove" a negative. (eg, "prove" to me you've never kayaked down the Colorado River. Can't be done unless you've videotaped every second of your adult life.) The court system understands this and places the burden on the plaintiff. The safeguards that the company I worked for had in place were enough to keep them from losing any copyright infringement case.
Anyway, enough about that. Designs of "utilitarian" goods such as flashlights are usually not copyrightable unless they incorporate some sort of non-utilitarian artistry that's not part of the functioning of the product itself. Patents are a whole 'nother subject, one I'm not versed in.
But I am surprised that a company would be so cool with unsolicited designs sent to them, since there are other legal avenues to go down for "theft" of those ideas.
None of this was intended to be legal advice