Interesting - I found these verses explaining about avataras in the Garga samhita canto 1
Text 16
shri-narada uvaca
amshamsho 'mshas tathaveshah
kala purnah prakathyate
vyasadyaish ca smritah shashthah
paripurnatamah svayam
Shri Narada said: In the Smriti-shastra the great sages who have Vyasa as their leader explain that the Lord descends in six kinds of forms: 1. amshamsha (a part of a part), 2. amsha (a part), 3. avesha (entrance into a jiva), 4. kala (a full part), 5. purna (full), and 6. paripurnatama (most full).
Text 17
amshamshas tu maricy-adir
amsha brahmadayas tatha
kalah kapila-kurmadya
avesha bhargavadayah
The amshamsha incarnations begin with Marici, the amsha incarnations begin with Brahma, the kala incarnations begin with Kapila and Kurma, and the avesha incarnations begin with Parashurama.
Text 18
purno nrisimho ramash ca
shvetadvipadhipo harih
vaikuntho 'pi tatha yajno
nara-narayanah smritah
The Smriti-shastra explains that the purna incarnations are 1. Nrisimha, 2. Rama, 3. Lord Hari, the ruler of Shvetadvipa, 4. Vaikuntha, 5. Yajna, and 6. Nara-Narayana.
Text 19
paripurnatamah sakshac
chri-krishno bhagavan svayam
asankhya-brahmanda-patir
goloke dhamni rajate
The paripurnatama form of the Lord is Shri Krishna, who is the original Supreme Personality of Godhead Himself. He is the master of countless universes. He is splendidly manifest in the realm of Goloka.
Text 20
karyadhikaram kurvantah
sad-amshash te prakirtitah
tat-karya-bharam kurvantas
te 'mshamsha viditah prabhoh
The amsha incarnations are said to oversee the execution of the Lord's mission (in the world). The amshamsha incarnations are understood to perform the work of executing those missions.
Text 21
yesham antar-gato vishnuh
karyam kritva vinirgatah
nanaveshavataramsh ca
viddhi rajan maha-mate
O great soul, O king, please know that in the various avesha incarnations Lord Vishnu enters (a jiva), executes His mission, and then departs.
Text 22
dharmam vijnaya kritva yah
punar antaradhiyata
yuge yuge vartamanah
so 'vatarah kala hareh
Millennium after millennium Lord Hari's kala incarnations teach and establish the principles of religion, and then disappear.
Text 23
catur-vyuho bhaved yatra
drishyante ca rasa nava
atah param ca viryani
sa tu purnah prakathyate
The purna incarnations are said to include the catur-vyuha incarnations. They are said to be the places where heroic powers and the nine rasas are seen.
Text 24
yasmin sarvani tejamsi
viliyante sva-tejasi
tam vadanti pare sakshat
paripurnatamam svayam
Others say that the form of the Lord where all powers and glories enter is His paripurnatama form, the original form of the Lord Himself.
Text 25
purnasya lakshanam yatra
tam pashyanti prithak prithak
bhavenapi janah so 'yam
paripurnatamah svayam
The transcendental qualities people see distributed among the Lord's purna incarnations are all present in the Lord's original, paripurnatama form.
Text 26
paripurnatamah sakshac
chri-krishno nanya eva hi
eka-karyartham agatya
koti-karyam cakara ha
The Lord's original, paripurnatama form is Shri Krishna and no one else. Coming (to this world) to execute one mission, He executes millions of missions.