I've had similar correspondence with the prolific Balasz Deri of Budapest. While searching for the parents of a relative of mine named Rebecca Spielberger Deutsch (born Zsarno/Zarnov 1846, married Leopold Deutsch, died Miskolc1890), I found Deri's extensive Deutsch tree on geni.com, in which he identified Rebecca as one of 7 children of an Izak and Esther Spielberger. When I queried him about his sources in January 2020, I got this reply:
I have no direct source about her parents either, as records of Zarnov nowhere seem to be available .
I have collected all data about Spielbergers some months ago, from Jewishgen, and - as far as I can remember now - I made the conclusion, based on some interesting ones about witnessing, that Isaak in Zarnov may be the same person as Isaak, whose children were born in Korlát and Novajidrány .
But this may not yet be fully proved, as even distant cousins may witness marriages. More patience and research is needed to confirm this yet .