Are there any differences between the years?

Like a simple connector or anything else that would indicate to me what period a harness came from? From what I understand, the part# may not help because it is the same p/n and can only be determined if from the new design from the date code on the harness.

Any way to tell accurately?

What model? There is certainly differences between the models/engines and there can be differences between the years - e.g. 92 400E is a different part number than 93+ and 320s have at least two different harnesses. But I'm not sure I understand what you're trying to get at. Are you looking at a harness that is not on a car? If it's installed on a car the only pertinent question would seem to be whether it's original or a replacement.

The best thing to do is look at the part # on the harnesses to see if they match as there are variations.

I always look at the part # on the harness to be replaced and get the dealership to look it up to see if the numbers are the same or have been substituted to another #.