Janissaryship

What led to Dziuba's "janissaryship"?

[...] but as "he loses status who stays in one place", he would have to sell two of his three offices (the scriptorship and the janissaryship totalling 1,400 ducats) in order to acquire his father's abbreviatorship.

Thus, Muṣṭafā b. Ḥasan, one such janissary, asked for a kadi warrant to verify his reʿāyā status on the following grounds: "I had served the sultan for a couple of years claiming janissary-ship. [...]"

Nevertheless, Janissaryship was expressed in a set of physical features [...]