Today I hit two places where the CNTTS apparatus claims that a manuscript has a correction, but where I had severe doubts in both cases. Not that I disagreed that the 'extra' words were written in between the lines, but not every interlinear addition is a correction.
The first is in minuscule 424, now helpfully accessible on the VMR (image of relevant page here).
The CNTTS apparatus gives for Galatians 3:19 μεσιτου] μωαεως 424cor. When I look at the actual image I think I can see μωσεως written above μεσιτου rather than μωαεως, which would save the addition from being nonsense. But is this really intended to be a correction? First of all, 424 is a commentary manuscript with lots of interesting things going on and with lots of scholarly material (explanation of the Hebrew names and other things I haven't had time to have a look at). It is not uncommon in such manuscripts to gloss certain words, and 'Moses' might be just such an explanatory gloss. There are two other glosses nearby. At 3:18 we find εχαριστο above κεχαρισται; and at 3:19 επηγγειλατο above επηγγελται, and according to Swanson this is both times the reading of minuscules 6 and 1739. Still, within 424 it is possible that we are dealing with a gloss that has made it into the main text of these manuscripts.
The second case was Galatians 4:18 where the CNTTS database has this: τεκνα] τεκνα θεου 1739cor (image here). Again the 'correction' in the shape of a nomen sacrum is there, but again, something different may be going on.
This time I suspect that it has to do with the start of the lectionary reading.
This is the main text of 1739 ὑμεῖς δέ, ἀδελφοί, κατὰ Ἰσαὰκ ἐπαγγελίας τέκνα ἐστέ. However, the start of the lectionary reading is indicated at κατα.
With our little addition we would get a perfect reasonable start for a lection. Κατὰ Ἰσαὰκ ἐπαγγελίας τέκνα θεοῦ ἐστέ.
I am not sure at all about this one, and would welcome anyone (preferably with some knowledge of lections) to shoot this idea down.