Good point.  It begs the question - did the Ziru Sirka name their Ishimkaruns?  Would the Vilani be aware that they were living in the era of "Ishimkarun So-and-so"?

It would be cool to think that that was so (and would, in part, explain the longevity of the Ziru Sirka).  However, a couple of points argue against this:

1.  In the Interstellar Wars era (especially as detailed in the GT sourcebook), the Ziru Sirka was rife with internecine struggles between Vilani Great Houses.  It is inconceivable that the Ishimkarun would be anonymous, when most of the province-level leadership were acutely aware of the need to maintain and expand personal and familial prestige.

2.  The Rebellion-era Ziru Sirkaa had no hesitation about appointing as its first restored Ishimkarun the very high profile (and member of a pre-eminent Noble House) Archduke, rather than than appointing an anonymous technocrat.

Cheers!

KenB