To be fair, I suspect only a small minority of viewers notice things like that. Limited budgets being what they are, I reckon it's better to spend money on getting the research right and getting the best contributors to weigh in.
The difference between the early -300 vibration gauge and that of the -400 can be demonstrated reasonably well using graphics, as the main difference is in the positioning of the indicator. Additionally, if I recall correctly, the misdiagnosis of which engine was having problems had more to do with insufficient conversion training - the -300 used bleed air from the right engine only, whereas the -400 used both.