1 Sam 12:6, LXX, ESV et al

I'm heading out to work and can't check this out but Samuel Driver has a textual commentary on Samuel, it's found on Google books.
It might provide some insight.

Rob

 

The NRSV doesn't say :"The Lord is witness." The NASB doesn't have :"The Lord is witness." And the HCS doesn't have :"The Lord is witness."

The TNIV is almost identical with the NET's reading, which doesn't have "The Lord is witness."

The NLT and GW don't have "The Lord is witness either.

Are you equating "The Lord appointed" with "The Lord is witness."?

 

Part of the witnesses of Origen's recension of the Septuagint add μαρτυς (witness) in 1 Sam 12:6, evidently against all the other witnesses and traditions. This addition is almost certainly a scribal harmonization to the same phrase "the Lord is witness" in the preceding verse (1 Sam 12:5), a kind of scribal error all too prevalent especially in the Greek tradition. For this reason it almost certainly is not original in 1 Sam 12:6.

Jonathan C. Borland

 

1 Samuel 12:4 καὶ εἶπαν πρὸς Σαμουήλ Οὐκ ἠδίκησας ἡμᾶς, καὶ οὐ κατεδυνάστευσας καὶ οὐκ ἔθλασας ἡμᾶς, καὶ οὐκ εἴληφας ἐκ χειρὸς οὐδενὸς οὐδέν.
5 καὶ εἶπεν Σαμουὴλ πρὸς τὸν λαόν Μάρτυς Κύριος ἐν ὑμῖν καὶ μάρτυς χριστὸς αὐτοῦ σήμερον ἐν ταύτῃ τῇ ἡμέρᾳ, ὅτι οὐχ εὑρήκατε ἐν χειρί μου οὐθέν• καὶ εἶπαν Μάρτυς.
6 καὶ εἶπεν Σαμουὴλ πρὸς τὸν λαὸν λέγων Μάρτυς Κύριος ὁ ποιήσας τὸν Μωυσῆν καὶ τὸν Ἀαρών, ὁ ἀναγαγὼν τοὺς πατέρας ἡμῶν ἐξ Αἰγύπτου.
1 Kingdoms 12:4-6

Whether you read Greek or not you can see how this might happen.
A copyist’s error from the Greek Septuagint could account for an insertion in the text of verse 6.
Another theory concerns the Septuagint as a translation, it's not a word-for-word translation.
The addition is certainly implied in the text whether it is implicitly there or not.

Rob