Ah, my bad, I jumped the gun. The part you had underlined in the old quote appears in all manuscripts (the part about pious tradition recounting that the Spirit is Second to the Son). The part that is in dispute is what comes after that. I knew what it was you were wanting to quote, but didn’t actually check to make sure that you quoted it.
Mark of Ephesus was at some point in the council of Florence aware that some manuscripts in Constantinople had the interpolation. His claim was that 1) the oldest manuscripts did not have it, 2) a majority of the manuscripts did not include the clause, and 3) Basil used that passage in a rhetorical manner, conceding that even if what Eunomius believed was true, it still didn’t lead to the necessity of a third nature (and that therefore even if the interpolation were genuine, it wouldn’t imply that Basil himself believed in it). Modern scholarship on the matter seems to have sided most especially with Mark of Ephesus on point 3), that the clause in question might not be an interpolation at all but a direct quotation of Eunomius (explaining its absence from some manuscripts and presence in others), meaning that Basil was using it as a rhetorical concession to show that Eunomius’ own beliefs did not logically lead to the conclusion that the Spirit must be of a third nature.