[1] (Adler cites comparable material ('cf.') in the Syntacticum Gudianum.) In fact this verb can be construed with the dative alone, but occurs more frequently with a preposition governing the dative or (as in the proverb cited) accusative.
[2] cf. Gregorius 2.15 (the metrical di\s pro\s to\n au)to\n ai)sxro\n proskrou/ein li/qon), and further in next note.
[3] Numbered by Meineke (380) and Kock (391-392) among the anonymous fragments of Attic comedy (Comica adespota), but not included in the more recent collection of Kassel & Austin. The second part of the quotation, from ptai/ein to o(mologou/menon, makes a good comic iambic trimeter, but the first part, though vaguely iambic, does not. Various emendations have been proposed to make the first part scan (see Kock ad loc.), but it may be that the actual source of this is not comedy but Polybius. In 31.11.5 (web address 1), repeated 31.12.2, Polybius records the advice he gave to Demetrius Soter of Syria "not to stumble twice against the same rock" by attempting to address the Roman senate a second time. The statement is identical to the present passage with the exception of the alternation between "twice" and "many times". The rest of the entry, "if one has an agreed-upon occasion," may be continuing the paraphrase of Polybius in more summary fashion: he goes on to advise Demetrius of the many occasions (kairou/s) he can take advantage of if he remains patient. If this is correct then the iambic meter of the last half is purely fortuitous. The whole phrase is repeated without a gloss at mu 972, where the headword of this entry ptai/ein is replaced by pai/ein ('strike').