@kmichel, the main reason for imprecision is two-fold: No information on how much insulin was loaded (all they "know" is at least approx 80U is in it, and the mechanism that detects fill past 80 is the same as the 50U remaining detection), and the imprecise nature of the shaft/spring contact.
The fact that this contact estimates that you've put at least 80U in when it makes contact, and then when it loses contact later estimates this occurs at around 50U should give you an idea of just how imprecise it is.
The pump is capable of very precise delivery accounting, which it must be, of course. The problem is, when it knows there is about 50U left, it can accurately count down from there, it's just that the 50 is a gross estimate, so we don't know if we're counting down from 50, 55, 65.
So counting pulses won't make any difference in terms of estimating actual remaining insulin. The only way to make this work is 1) design in an accurate measuring mechanism (very expensive), 2) require user to enter insulin put in pod into PDM (too error-prone), 3) require a precision fill so the same precise (to the unit) amount is required to activate the pod (too inflexible).
What we have is the best compromise, I think.