The problem is where does it come from Pat - each point in the SPJ has a Date and Time, but a surface could be measured over a period of a week for example - so what date do you use. If you then come back a month later and add 3 points to the surface, does the date change by a month when you import it again. This is why we let you set it so you can put it where you want it. That date also puts the surface in the Volume hierarchy (Original comes before Work in Progress comes before Design and then Date of Surface places a later Work In progress later in the hierarchy after an earlier one of the same classification.
The Date of the file cannot be used because the Work Order may be opened many times after the surface was measured changing the Date and Time, and it gets dated and timed as you sync it to TCC and then from TCC to the laptop etc. so it is not reliable. The point data is an option but again that could be the First Point, Last Point or the Average Date and Time (some work to analyze and compute, and none are reliable overall unless you survey everything in an afternoon for example and only you know that
This is why it is as it is - we determined that the only reliable way to do this was to allow the user to set the date or modify the date.
Alan