Actually the Greek word
plerophoreo can have several meanings, depending on the context. One of those meanings is "fully convince" or "fully believe". So the KJV translators were certainly NOT in error when they put down "most surely believed". In fact, contextually it is more appropriate than "fully accomplished" since Luke wanted Theophilus to know "the certainty of those things".
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Strong's Concordance
plérophoreó: to bring in full measure, to fulfill
Original Word: πληροφορέω
Part of Speech: Verb
Transliteration: plérophoreó
Phonetic Spelling: (play-rof-or-eh'-o)
Short Definition: I carry out fully, fully convince
Definition: (lit: I carry full), (a) I complete, carry out fully, (b) I fully convince, satisfy fully, (c) I fully believe.
Thayer's Greek Lexicon
STRONGS NT 4135: πληροφορέω
πληροθορηθεις, persuaded, fully convinced or assured,
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If you are going to cite Thayer's Lexicon, you should cite the full discussion of the word in question!
First Thayer agrees that as used in Luke 1:1,
πληροφορέω means accomplished or completed. (See geeen highlight)
While Thayer does indeed say
πληροφορέω can mean fully persuaded he states conditions (see blue highlight)
We do NOT find τινα ....... [FONT=lucida\ console]ἐν[/FONT] with the dative of thing) in Luke 1:1.
NT:4135
NT:4135
πληροφορέω, πληροφόρω: (1 aorist imperative
πληοφόρησον, infinitive
πληροφορησαι Rom 15:13 L marginal reading); passive, present imperative plhroθορείσθω ; perfect participle
πεπληροφορημεωος ; 1 aorist participle
πληροφορηθείς); (from the unused adjective
πληροθορος, and this from
πλήρης and φέρω); to bear or bring full, to make full;
a. to cause a thing to be shown to the full:
τήν διακονίαν , i. e. to fulfil the ministry in every respect, 2 Tim 4:5 (cf. =
πληροῦν τήν διακονίαν, Acts 12:25); also
τό κήρυγμα, 2 Tim 4:17.
b. "to carry through to the end, accomplish: πράγματα πεπληροφορημεωα, things that have been accomplished (Itala and Vulg. completae), Luke 1:1 (cf.
ὡς ἐπληρώθη ταῦτα , Acts 19:21) (cf. Meyer edition Weiss at the passage).
c. τινα, to fill one with any thought, conviction, or inclination: (Rom 15:13 L marginal reading (followed by [FONT=lucida\ console]ἐν[/FONT] with the dative of thing): others,
πλερόω, which see, 1); hence, to make one certain, to persuade, convince, one (
καί ὅρκοις πληροθορησαντες Μεγαβυζον , extracted from Ctesias (401 B.C.) in Photius, p. 41, 29 ((edited by Bekker); but on this passive, see Lightfoot as below)); passive, to be persuaded, Rom 14:5;
πληροθορηθεις, persuaded, fully convinced or assured, Rom 4:21; also peplhrouorήμενοι, Col 4:12 L T Tr WH;
οἱ ἀπόστολοι ... πληροθορηθεντες διά τῆς ἀνστάσεως τοῦ κυρίου Ἰησοῦ Κριστοῦ καί πιστωθενθες ἐν τῷ λόγῳ τοῦ Θεοῦ, Clement of Rome, 1 Cor. 42, 3 [ET]; frequent so in ecclesiastical writings; to render inclined or bent on,
, Eccl 8:11 (cf. Test xii. Patr., test. Gad 2). The word is treated of fully by Bleek, Brief an d. Heb 2:2, p. 233ff; Grimm in the Jahrbb. f. Deutsche TheoI. for 1871, p. 38ff; (Lightfoot's Commentary on Col 4:12. Cf. also Sophocles' Lexicon, under the word.)*