Before the molecular [by Bernasconi et al.] work there were also two different interpretations dealing with these two species:
S. suilla (=S. taeniopa) and S. ordinata [Sifner, 1975, 1995]
S. suilla and S. taeniopa (=S. ordinata) [Gorodkov, 1986]

Sifner (2008) decided to accept the name taeniopa after all and he refers to Gorodkov's list of 1986: "Synonymized by GORODKOV (1986: 34)". However, I think he made an error in accepting that Gorodkov's listing in the catalogue as synonymization. Gorodkov used the name taeniopa earlier for a valid species (Insects of Mongolia, not available to me). At the same time he may not have been aware of ordinata as separate species or already accepting that as synonym of taeniopa. In either case, Sifner formally synonymized suilla and taeniopa in 1975 and my assumption is that Gorodkov, whilst preparing the 1986 catalogue, was not aware of it or chose to ignore it since he does not state a reference where the synonymization by Sifner is refuted.
For the name taeniopa to become available again it should have been resurrected from synonymy or someone should have stated in no uncertain terms that Sifner was wrong to synonymize these species in 1975. As far as I know, neither was done and, in my view, Gorodkov, 1986 does not do it either.

So [...] how it came to be that the name taeniopa was used [in the molecular works]. I assume it can be traced back to the keys used for identification of the species. Are you aware which keys were used to identify the species in the molecular work?

Perhaps a bit academic but it seems a valid question nevertheless since no-one seems to have examined the type of taeniopa to see with which species it actually agrees...