Yeap it may be worth another try. I'd love to visit Istanbul one day, but work doesn't permit at present.
The Nufus Defteri (Population Records) essentially are listings of the males of a community and their sons, giving descriptions about them e.g. nicknames, dates of birth or ages at time of the population census and other remarks including dates of death, or whether an individual moved to another community. Women weren't recorded until much later in the 1880s or 1890s if I'm not mistaken.
There are also Temettuat Defteri, essentially tax records of the males of a community, and also Cizye records (a tax on the Christian male subjects of the Ottoman empire). They were taken to determine taxes due, and served as an informal register of the males of a community.
My ancestors were Greek Cypriots from Cyprus, and as you would be aware the Ottoman Empire controlled Cyprus from 1571-1878, so there are records pertaining to communities that are invaluable to both Greek and Turkish Cypriot researchers, which are held in the Ottoman archives in Turkey.
Regards,
Anthony