From the translation of MN 72
That’s why a Realized One is freed with the ending, fading away, cessation, giving up, and letting go of all conceiving, all churning, and all I-making, mine-making, or underlying tendency to conceit, I say.”
Here, the Pāḷi says that the tathāgata is ‘anupādā vimutto.’ I don’t see a correlate to ‘anupādā’ in the above translation. Doing a quick search, at DN 15 you translate this phrase as " freed by not grasping."
From a note on MN 72:
Here “realized one” (tathāgata ) pertains to any arahant, as at SN 54.12. The Pali commentary and one of the Chinese parallels here (SA2 196 at T ii 445a18) agree in saying that a “living being” (satta ) is meant. However, tathāgata and satta are exact verbal parallels: tathā (“real”) + gata (“come to the state of”) and sa (“real”) + tta (“state of”). Thus it seems likely that this was originally intended as a mere verbal gloss to resolve the compound.
As far as I know, the commentarial tradition interprets the tetralemma on the Tathāgata as circling around the idea of a ‘true being’ continuing, being destroyed, both, or neither. I think that when the commentary uses the term ‘sentient being’ here, it means it in the substantialist sense as at SN 5.10, similar to ‘self’ (attā, puggala, satta, jīva, etc.). The commentary apparently makes the distinction between how some use the term ‘tathāgata’ with the meaning of a true being, vs. the Buddha’s use which is not meant to refer to a self or substantial sentient being. 
I assume that this is also a case in the Chinese parallels of commentarial exegesis entering the Āgama transmission, either in the Indic originals or in the Chinese translation to clarify the meaning. It says “眾生神我” with the word for “sentient being” and also two characters meaning “self” (神 + 我) next to each other. In fact, Ven. Anālayo cites this in his ‘Saṁyukta Āgama Studies’ as a case of similarity between later exegesis in the Pāḷi and Āgama translations.
I did find it interesting though that you pointed out how ‘tathāgata’ and ‘satta’ have near identical etymologies! Of course, the idea of ‘satta’ assuming a self can be traced all the way back to the Ṛgveda and the idea of the gods being ‘sat’ because of their being immortal.
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