Well, this thread has gone a bit off on a tangent...
UL is quite adamant ... neither FPE nor Zinsco ever 'lost' their listing. Both firms continued to make listed products to the day they closed their doors. As far as UL is concerned, they closed their doors simply for business (or lack thereof) reasons.
Indeed, the parent of Square D continues to make, and sell, FPE breakers in Canada.
UL decided, some years back, to go the "ISO9000" route. As a consequence of this act, they inadvertently opened up their market to competing testing firms. ETL is one such firm.
Whether a firm chooses to do business with UL is their decision, and may be influenced by many factors.
Whatever a UL listing may mean ... NEVER confuse it with being any sort of stamp of quality. Some of the most absurd products have managed to pass the appropriate tests. The tests are for 'safety,' not for effectiveness, or quality.