You seem to have stumbled upon a particularly controversial locus, and several versions of the Latin, as well as different translations can be found.
Here is D. J. W. Olshausen's German translation, 1811:
Einstweilen hast Du viele, deren Schriften man wohl nur nicht in gehöriger Ordung lieset.
In the mean time, you have many, whose writings, I think, people are just not reading in the right order.
Then A. Pauly (that Pauly!) in his 1833 German translation writes:
Inzwischen hast Du ja Viele, deren Schriften man wohl, nur nicht in gehöriger Ordnung liest.
In the mean time, you have many, whose writings are read well enough, but not in the right order.
… and adds a footnote:
So Olshausen. Der Sinn der Worte: Interim multos habes, quorum scripta nescio an satis ordinent, ist mir zweifelhaft. Gebrauchte vielleicht Seneca nescio an gegen den Gebrauch der Späteren affirmativ, und wollte sagen: – „deren Schriften den Geist vielleicht schon genugsam zu ordnen vermögen“ –?
According to Olshausen. The meaning of the words: Interim multos habes, quorum scripta nescio an satis ordinent, is dubious to me. Did Seneca perhaps use nescio an affirmatively, contrary to the usage of later writers, and wanted to say: – “whose writings are perhaps able to put the mind in proper order” –?
Actually I think he does not exactly follow Olshausen here, but that is a minor squibble that has more to do with German than Latin. And why in the world would Seneca not use nescio an affirmatively, as every textbook of Classical Latin teaches us? (Pauly gets schooled on this point here by one A. E. Schnell of Bern.) But note the most important point: Pauly seem to have thought the verb was active! They presumably had Seneca editions which said ordinent.
And note how his own suggested translation not only changes the emphasis of nescio an to the affirmative; he completely changes the meaning and is in line with your Loeb translation: the subject of ordinent is now not some anonymous public as with Olshausen, but the scripta.
Another philologist in possession of such an edition was the eminent J. N. Madvig, to whom, however, ordinent makes no sense at all, but who suggests ordines instead:
Interim multos habes, quorum scripta nescio an satis ordinent. Quem aut quid? et quid hoc est, scripta philosophorum aliquid aut aliquem ordinare? Scribendum videtur: quorum scripta nescio an satis ordines. Sume in manus indicem philosophorum (ut eo in ordinandis scriptis utare). Cum scriptum esset ordinesume, factum est ordinent.
Thus, my best guess would be that the Loeb translation is also based on the active form, and the answer to Madvig's quem aut quid? is something like: mentem vel cogitationes lectoris. But the passive form, which seems to have been adopted by editors eventually (for whatever reason), is incompatible with that translation. Both the active and the passive form can be translated as “which I think are ordered well enough” (by the general public), which can be understood as most readers putting the writings in the right order for reading them (or perhaps for ranking them?).
