There are three main concerns regarding these umlauts:
1. A complete and accurate list of all umlauts must be compiled.
2. The dating of the umlauts must be carefully evaluated.
3. The MS evidence of the presumed variants must be catalogued and analysed.
The Catholics have the highest number, about trice as much as the Gospels. It might be interesting to check if the nature of the variants in Acts or the Catholics or Paul is different from the Gospels.
My preliminary spot checks show no clear differences in the various NT parts. In the Gospels there are variants from D and/or Byz. Ok, quite evident, what else should there be? Caesarean only. In Acts there seems to be an even distribution between readings supported by D alone, Byz alone and D+Byz. The apearance of those "D alone" readings in Acts is interesting. In the Pauline letters I noticed some readings which are supported by P46 as main witness. Well, only spot checks and only with NA 26.
In general there is no CLEAR pattern in the witness support for the various umlauts. We have support from
- D only
- Byz only
- D + Byz
- P46 only
- some minuscle MSS only.
IMHO this indicates that not one single MS has been used for comparison, but more than one. At least not one MS which fits such a pattern is extant today. This makes the whole umlaut thing even more mysterious. Maurice Robinson suggests that each major NT section Gospels, Acts/Catholics and Paul have been compared with a different MS.
While comparing the MS on my own I found it quite time consuming. So, why should someone compare the complete NT with several MSS so carefully? This is extremely time consuming and laborious. I have difficulty in imagining that this has been done for intern library usage only. Maybe it was for some "official" purpose?
If we assume that at least some of the umlauts have been added by a later scribe, it might be interesting to check, if the umlauts which are not reinforced (and are eventually earlier) show a different pattern than the rest.