Well, both my Kubicki Ex Factors (#1777 and #1659) are 1989 models. By listing their year and serial numbers, you can deduce that they are "cross over" models, made after Phil Kubicki entered into partnership with Fender but still constructed from the original parts (the 18V preamp, namely).
There actually isn't a huge difference between the different basses (Pre-Fender, crossover, Fender era, post Fender), aside from the fact the Fender era basses had a 9V preamp with fewer presets. When Phil joined Fender it was simply to get his basses into a new market, using Fender's nationwide dealer network where previously you had to buy directly from Phil. Unless you're an experienced Kubicki player you'll find it hard to spot the differences between them save for the preamp.
However, the "era" tha bass was made does have a bearing on the value. Pre-Fender (the earliest models) are considered the most desireable, whereas Fender era models are worth a bit less. I suppose I am happy to have owned two crossover models, made with the original parts in the original workshop, they are after all the rarest models of all!