I found the following information in a rather old book and have not been able to verify this, but it looks interesting.
According to Tregelles' intro to his text of Revelation (1844), the Codex Corsendoncensis (I believe this is Gregory-Aland minuscule 3, right?) reads as follows in 2 Cor 8:4-5
δέξασθαι ἡμᾶς ἐν πολλοῖς τῶν ἀντιγράφων οὕτως εὕρηται καὶ οὐ καθὼς ἠλπίσαμεν.
The first two words δέξασθαι ἡμᾶς are an addition found in some mss, while everything from καὶ οὐ ... onwards is part of the regular text of 8:5. That leaves the words 'ἐν πολλοῖς τῶν ἀντιγράφων οὕτως εὕρηται' ('such it is found in many copies'), referring apparently to the addition of δέξασθαι ἡμᾶς. A good example of a marginal comment in the exemplar that was included in the main text. This phenomenon must have happened more often.