Many thanks for posting the two species described in You et al. (please forgive the incorrect order I used - I don't know many Chinese characters - I do know the characters for Li and Wang, but will have to try and remember You for future reference). Incidentally, Prof. Li attended the recent 1st South East Asian Lepidoptera Conservation Symposium held by Kadoorie Farm & Botanic Garden. He has helped with some species identifications already from my thesis (and subsequent) collection, and has taken some voucher material to work on back in Tianjin - mostly Gelechiidae and Oecophoridae. We will be doing a few joint papers over the next year or so to list the HK species, including several currently undescribed.
As to the Eristena - the most obvious difference appears to be the medial fascia on the forewing, which is virtually continuous and heavily shadowed in the Lantau specimen, whereas the Japanese specimens illustrated on the internet of E. argentata have the medial fascia broken into three sections with very little shadowing; the apical side of the post-medial strigula is not lined on the Lantau specimen (and the strigula appears broader). There are subtle differences on the abdominal banding as well. As we both noted, a specimen will be needed to confirm, via its genitalia, the actual identity of the Lantau species.