= Aelius Dionysius sigma12, Photius sigma158 Theodoridis.
The entry makes no effort to define the words in question. Its only concern is whether in proper Attic dialect the perfect forms of certain verbs exhibit a sigma at the end of their stems prior to the inflectional endings. The primary pair are, respectively, perfect middle indicative, third person singular, and perfect middle participle, masculine nominative, of the verb sw/|zw. If the words are extracted from literary texts, possible sources include tragedy and Plato (e.g. for se/swtai, Aeschylus, Seven against Thebes 812, Euripides, Iphigeneia at Tauris 607, Plato, Critias 109D; for seswme/nos, Aeschylus, Persians 503, Sophocles, Ajax 1129, Plato, Laws645B). Both, in any event, are less common than their sigma-endowed counterparts se/swstai and seswsme/nos, but the chronological distinction asserted here is difficult to corroborate. So too with the other forms in the entry. On whether the assertions of the entry are correct or not, Theodoridis cites Cobet, Mnemosyne 11 (1862): 340, Kontos *)aqhna= 17 (1905): 440-441, Kühner-Blass I.2.544-545, and others.
[1] Thucydides 1.6.5; rather than the more common diezwsme/noi with the sigma.
[2] That is, they write this and similar forms with the sigma.
[3] Who 'they' are has now, for this last point, become ambiguous. Perhaps the sense is that the 's' is normally left out of these words in all periods, but that would be an assertion difficult to corroborate, as forms of these words with and without the sigma are equally well attested.