1 John 2:20 in the KJV, following the Byzantine textual tradition, reads:
But ye have an unction from the Holy One, and ye know all things (οἴδατε πάντα)
The NASB and many modern translations, following the Alexandrian text-type, reads:
But you have an anointing from the Holy One, and you all know (οἴδατε πάντες)
The reading οἴδατε πάντες is followed by א B P Ψ copsa. The reading οἴδατε πάντα is found in A C (049) 33 1739 Maj it syr copbo.
Commenting on this variant, Philip Comfort noted:
The two readings could have easily been confounded for each other in the transmission process inasmuch as there is only a two-letter difference (παντες/παντα) between the two. Furthermore, both readings have decent documentary support and are exegetically defensible. According to the WH NU reading, John was affirming that all the members of the church community know who is a genuine believer and who is not (see 2:19): “you have an anointing from the Holy One and you all know.” The anointing that each and every one of the believers has received helps them to discern the false teachers from the true. Thus, the emphasis is on shared communal knowledge. According to the reading of the variant, the emphasis is on the anointing and how it enables believers to know everything: “you have an anointing from the Holy One and you know everything.” The term “anointing” describes the impartation of the Holy Spirit (see Isa 61:1). Christians, indwelt by the Holy Spirit, are joined to Christ, “the Anointed One,” and share in his anointing (2 Cor 1:21-22). Therefore, Christians can know all things with respect to truth and falsehood. (Philip W. Comfort, New Testament Text and Translation Commentary: Commentary on the variant readings of the ancient New Testament manuscripts and how they relate to the major English translations [Carol Stream, Ill.: Tyndale House Publishers, Inc., 2008], 775)