Bhakta: "Why Balarām’s birthday is not celebrated but Nityānanda’s and Advaita’s days are?"
Advaita Das: "None of these tithis are in Hari Bhakti Vilāsa - there is Janmāṣṭamī, Nṛsiṁha caturdaśī and Rāma Navami. Not even Rādhāṣṭamī is official - they are adopted according to bhāva (sectarean feelings). In our family we do a big utsava on Advaita Saptami and Shiva Rātri, but those things are hardly observed in ISKCON at all. Reversely, ISKCON is doing big things on "Balarām Purnima" which we do not even recognize at all.
Bhakta- “I see. And the date of Balarām’s birth, though not celebrated, is different from the one given by IGM. At least according to the calendar I got from Rādhākuṇḍa....that date is two days before Rādhāṣṭamī.”
Advaita Dās- “We are not devotees of Balarām anyway, but of Kṛṣṇa, but it is a bit intriguing. This is from Garga Samhitā 1.10.27-28-
atha vraje panca-dineṣu bhādre tithau ca ṣaṣṭhyāṁ ca site budhe ca
uccair grahaiḥ pancabhir āvṛte ca lagne tulākhye dina-madhya-deśe
sureṣu varṣatsu su-puṣpa-varṣaṁ ghaneṣu muncatsu ca vāri-bindūn
babhūva devo vasudeva-patnyāṁ vibhāsayan nanda-gṛhaṁ sva-bhāsā
“Then, in Vraja, after five days, in the month of Bhādra (August-September), on the sixth day of the bright fortnight, when Mercury, five exalted planets, and the constellation Libra were on the horizon, at midday, as the demigods showered a beautiful rain of flowers and the clouds sprinkled drops of water, (Śrī Baladeva), illuminating Nanda's home with His splendor, was born from Vasudeva's wife (Rohiṇī).”
Advaitadās: “ISKCON and Gauḍīya Maṭha are not alone in observing Śrāvaṇa Pūrṇimā as Baladeva’s birthday; the Brajabāsīs also do it. Problem is, I have little faith in Garga Samhitā.”