Conclusion
On the point about the dating of versions of the Heart Sutra referred to in Woncheuk's commentary we need first to address the issue of "older texts". Crucially, Lusthaus says earlier in his article,
"We have no dates of other background information on when or where the two commentaries were written... We don't know for certain even if these commentaries were written before or after [Xuanzang's] death, though my sense is that they were written after." (2003: 66: emphasis added)
The conjecture by Lusthaus that the commentaries he is discussing were written (i.e. composed) after the death of Xuánzàng is important in assessing his claim that the alternate readings found in them amount to a text from a much earlier period, particularly contemporary with Kumārajīva in the early fifth century.
We've seen that when Woncheuk mentioned old texts" (舊本) he was in fact directly referring to a number of other sutras in which Avalokiteśvara plays a prominent role. So Lusthaus's conclusion that it would be "natural" in this context to conclude that this referred to the Heart Sutra looks wrong. We've also seen that his attempt to connect Woncheuk's text with Kumārajīva fails. Lusthaus's challenge to Nattier's theory falls well short of its mark.
What we're left with is evidence of multiple versions of the Heart Sutra, probably around the time of, or not long after, the death of Xuánzàng. No texts with the readings evinced by Woncheuk, in either Chinese or Sanskrit are extant. Thus there is no good case for pushing back the date of composition of the Heart Sutra before Xuánzàng. On the other hand, the evidence for multiple versions at this time is intrinsically interesting in terms of the history of the text. And in drawing attention to these early commentaries. Lusthaus has made an valuable contribution.
Nattier's thesis on the origins of the Heart Sutra certainly has stronger and weaker points. However, it is beyond reasonable doubt that the Heart Sutra per se began life in China as a compilation of extracts from Kumārajīva's《摩訶般若波羅蜜經》(T233) or possible the commentary on it 《大智度論》and probably other texts including the Mahāmegha Sūtra (possible source of the dhāraṇī). And her arguments about the attribution and dates of T250 and T251 largely stand. Neither seem to be the product of authors to which they were attributed in the 8th Century.
~~oOo~~
Bibliography
Conze, Edward. (1978). The Prajñāpāramitā Literature. Tokyo, The Reiyukai.
Hyun Choo, B. (2006) 'An English Translation of the Banya paramilda simgyeong chan: Wonch'uk's Commentary on the Heart Sūtra (Prajñāpāramitā-hṛdaya-sūtra)' International Journal of Buddhist Thought & Culture. February 2006, Vol.6, pp.121-205.
Lusthaus, Dan. (2003) 'The Heart Sūtra in Chinese Yogācāra: Some Comparative Comments on the Heart Sūtra Commentaries of Wŏnch’ŭk and K’uei-chi.' International Journal of Buddhist Thought & Culture. September, Vol. 3: 59-103.
Nattier, Jan (1992). 'The Heart Sūtra: a Chinese apocryphal text?' Journal of the International Association of Buddhist Studies. 15 (2) 153-223. Online:
http://archiv.ub.uni-heidelberg.de/ojs/ ... /8800/2707
Shih, Heng-Ching & Lusthaus, Dan. (2006) A Comprehensive Commentary on the Heart Sutra (Prajnaparamita-hyrdaya-sutra). Numata Center for Buddhist Translation & Research.
Tanahashi, Kazuaki. (2014) The Heart Sutra: A Comprehensive Guide to the Classic of Mahayana Buddhism. Shambhala.