One nondual Reality, three designations
Knowers of truth call the nondual knowledge Brahman, Paramatman, Bhagavan: 'brahmeti paramatmeti bhagavan iti sabdyate' (SB 1.2.11).
Concept
Brahman
ब्रह्म
Brahman is the supreme Reality of the Upanishads and Vedanta — 'satyam jnanam anantam': the one attributeless existence-consciousness-bliss from which the world proceeds and whose realization is liberation, described both impersonally and personally. In the processed verses the Bhagavata's ruling is: the nondual Truth the knowers declare is expressed by three names — Brahman, Paramatman and Bhagavan: 'brahmeti paramatmeti bhagavan iti sabdyate' (SB 1.2.11); sattva is called 'the vision of Brahman' (1.2.24).
Śrīmad Bhāgavata Mahāpurāṇa 1.2.11 — Sanskrit Wikisource (pinned oldid=110173)
Brahma-darshana: negating both sat and asat superimposed by avidya
'Yatraime sad-asad-rupe pratisthidhe sva-samvida avidyayatmani krite iti tad brahma-darsanam' (SB 1.3.33).
Pure, absolute knowledge, without quality, eternal and without a second
'vishuddham kevalam jnanam pratyak samyag avasthitam, satyam purnam anady-antam nirgunam nityam advayam' (SB 2.6.39); the stilled sages know it, false reasonings hide it (SB 2.6.40).
Brahman — nondual with — Paramatman
The knowers of reality declare one nondual Truth, designated both 'Brahman' and 'Paramatman': 'brahmeti paramatmeti bhagavan iti sabdyate' (SB 1.2.11). Evidence: EXPLICIT (advayam).
Brahman — nondual with — Krishna
The same nondual Truth is designated 'Bhagavan' (SB 1.2.11) - the Lord whom the Bhagavata identifies as Krishna, Lord of the Satvatas (SB 1.1.12): one Reality, three designations, of which Bhagavan is the most complete. Evidence: EXPLICIT for the shared nondual tattva; nuance preserved in the description.