The terms "trial strike", "die trial", "die adjustment strike", and "set-up piece" are all untenable and represent wishful thinking. Unless you were there to witness the strike, there is no way to determine the cause of the weakness. My studies of multi-error weak strikes, the distribution of weak strikes among different denominations, and the relative strength of these strikes indicate that the vast majority are the product of spontaneous equipment malfunction. It's also clear that the majority owe their appearance to excessive minimum die clearance (insufficient die approximation). The dies either fall out of adjustment or something interferes with normal die approximation. These malfunctions sometimes occur quite suddenly, are often short-lived, and sometimes correct themselves spontaneously.
Error coin writer and researcher.