We have been trying to make sense of the first sentence of 7,4,3. What if we related it to what immediately precedes? I.e. 7,4,2.
We would get this:
"This harbour forms with another harbour called Ctenus Limen an isthmus forty stadia in width; and this is the isthmus that encloses the Little Chersonesus, which, as I was saying, is a part of the Great Chersonesus and has on it the city of Chersonesus, which bears the same name as the peninsula.
3 This city was at first self-governing, but when it was sacked by the barbarians it was forced to choose Mithridates Eupator as protector. He was then leading an army against the barbarians who lived beyond the isthmus as far as the Borysthenes and the Adrias; this, however, was preparatory to a campaign against the Romans.
So, then, in accordance with these hopes of his he gladly sent an army to Chersonesus, and at the same time carried on war against the Scythians, not only against Scilurus, but also the sons of Scilurus — Palacus and the rest "
What if the "isthmus" of 7,4,3 is not Perekop (as the editorial note suggests), but, as in the immediately preceding text, "the isthmus that encloses the Little Chersonesus which... has on it the city of Chersonesus, which bears the same name as the peninsula"? Everything would fall into place without the need to postulate an undocumented expedition at some point other than Chersonesos.
****Two more things. If one retains the understanding that isthmus=Perekop (in 7,4,3) there is the Strabo text in 7,4,5 which designates most of the Crimea plus the land north of Perekop "up to the Borysthenes" as "Little Scythia", and also indicates by implication that north of this isthmus "Little Scythia" actually reaches the Tyras. Which makes an emendation of "Adrias" to "Tyras" (as the land of the assaulted "barbarians" immediately identified as Scythians in 7,4,3) plausible.
Furthermore: Strabo (also in 7,4,5) talks of another "Little Scythia" (the one formed by Scythian migrants who crossed the Tyras and Ister(Danube) into Thrace). Now if one compares the information to be found in Pliny about this second territory (with a whiff from Ps.Skumnos) one gets really interesting stuff. Ps. Skumnos states that the boundary between Scythians and Thracians in Thrace runs near Dionysopolis (today's Bulgarian Balchik). Pliny gives lots of details about the land once ruled by the Scythae Aroteres from around Dionysopolis to the Danube. Not least of which is the fact that there was a river Zyras at the boundary of this southern Scythia. So another emendation might be possible: not "Tyras" but "Zyras", actually more faithful to the extent of the Skilur holdings in 110 BCE.*****