here is more from Ferdowsi's Shahnameh with referal to nationality/ethnicity:

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Aba har savari parstandeh siz, Tork o ze Rumi va az Parsi.
http://shahnameh.rec...m=494&page=21#1
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Ze panjah baz avaridand siz, ze Irani o Rumi o Parsi
http://shahnameh.rec...m=476&page=19#2
This one could mean Parsi refers to inhabitants of Persia(modern Fars Province in Iran) and Irani perhaps refers to non-Pars(ie. other Aryans like Parthians(Pahlavani/Part-ha), Hyrcanians(Gorgani), Bactrians(Balkhi),etc.
other examples of use of word Iranian from same source:
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Cho tang andar amad ze shahi sokhan, ze Iraniyan hark oo bad kohan

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chenin goft manzar be Iraniyan, ke khaham ke danam be sood o ziyan
I don't know why Ferdowsi didn't use the word Tajik because during the Tahirid and Samanid Dynasties, persian people in Eastern Iran(modern Khorasan province & modern Afghanistan) as well as Central Asia(modern Turkmenistan, Tajikistan, Uzbekistan)
were referred to as
Tajik people of the crown in order to be distinct from the Turkic population because the royal families of Tahirid and later Samanid were Persians.
It must be noted that Ferdowsi wrote Shahnameh during reign of Sultan Mahmud Ghaznavi(who was a Turkmen from the Ghaznali clan of the Kayi Tribe), perhaps the word Tajik became prohibited to be used as persians no longer held power, does anyone know anything whether the word Tajik was still in use?