It is known that Shuklya Yajurveda was taught to great Yajnavalkya by Survya deva. Then Yajnavalkya Rishi taught it to his many shishya. This resulted in 16 shakhas. My question is if Yajnavalkya taught what he learnt from Survya deva as it is to his shishya how come there are 16 shakhas instead of 1. There can be 2 possibilities. First Yajnavalkya learned all 16 shakhas from Surya deva. Second one is that all the 16 shishyas altered it and created their own shakha. Which one is right?
As you have said in your question there are 16 recensions or Shakhas of Shukla Yajurveda , and your query is -
how come there are 16 shakhas instead of one.? and Yajnavalkya learned all 16 shakhas from Surya deva. Second one is that all the 16 shishyas altered it and created their own shakha.
The exact answer of your question is given in a Srimad bhagavata Purana Canto 12- Chapter 6 - Shlokas 73-74 which mentions the story of Yajnavalkya Rishi receiving a new never known Yajurveda from sun god. Here the number of recensions mentioned are 15 instead of 16 by you in your post.
एवं स्तुत: स भगवान् वाजिरूपधरो रवि: ।
यजूंष्ययातयामानि मुनयेऽदात् प्रसादित: ॥ 73 ॥
यजुर्भिरकरोच्छाखा दशपञ्च शतैर्विभु: ।
जगृहुर्वाजसन्यस्ता: काण्वमाध्यन्दिनादय: ॥ 74॥
evaṁ stutaḥ sa bhagavān vāji-rūpa-dharo raviḥ
yajūṁṣy ayāta-> yāmāni munaye ’dāt prasāditaḥ
yajurbhir akaroc chākhā daśa pañca śatair > vibhuḥ
jagṛhur vājasanyas tāḥ kāṇva-mādhyandinādayaḥ
Sūta Gosvāmī said: Satisfied by such glorification, the powerful sun-god >assumed the form of a horse and presented to the sage Yājñavalkya yajur-mantras > previously unknown in human society. From these countless hundreds of mantras of the Yajur Veda, the powerful sage > compiled fifteen new branches of Vedic literature. These became known as the > Vājasaneyi-saṁhitā because they were produced from the hairs of the horse’s mane, and they were accepted in disciplic succession by the followers of Kāṇva, Mādhyandina and other ṛṣis.
In above shlokas it is mentioned that Rishi yajnavalkya received a brand new yajurveda never known to any human being ever from sun god and he himself compiled those 15 branches of yajurveda . Those 15 shakhas or recensions are known as vajasaneya Samhita and those were accepted by the followers of Kāṇva, Mādhyandina and other ṛṣis.
Here is Gita Press translation of the same.
Currently there are only two recensions available to us i.e kanva and Madhyandina.
So it was rishi Yajnavalkya himself who created those 15 recensions. We can read the Story of yajnavalkya from bhagavata purana Slokas 59-74