Ethnologue errs with West Germanic languages.

Sourcesa are diverging. Many do not mention the "German" group of the 2nd list, some more modern ones call it "Dutch-German", older ones call it "German" or very similar. Nothing I know of is backing SIL/Ethnologue.

ISO 629-3 is the standard, and of course does not say anything about language families. Ethnologue is not a standard, makes obviously wrong claims here and there, but is published by the same organisation (SIL) as ISO 639-3 is. I do send them e-mail about their errors and omissions, and they corrected some things already, but that took long time.

Since Ethnologue is not a standard, I would not give much about not following it, if there are good sources showing that they err.

We do not follow it, e.g. by correctly putting Limbourgish (of the Dutch and Belgish provinces Limbourg) to its Low Franconian relatives, and not - like Ethnologue does - into Rhine-Franconian, despite the fact that there is a city and bishopric called "Limburg" near Frankfurt in Rhine-Hesse, too, where a Rhine-Franconian Variety is spoken.

OK, let me phrase it differently: I want data about languages or their relation to adhere to that published by standard bodies.

I've written another lengthy e-mail to SIL telling them of about a dozen or so points where they deviate from published academic opinions in the West Germanic tree. Some are apparent and obvious errors which they certainly will correct in the next edition. Two deviations are worth to mention here. One cannot be called an error, imho:

1. Ethnologue has 4 language groups of West Germanic. Standard publications of the Dutch-German linguist community have one level of grouping in between, Anglo-Frisian, and Dutch-German (the latter often only called German) which Ethnologue skips. Imho you can make that, it's only unusual.
2. In the High German group, you have the big subgroups Middle German (aka Central German) and Upper German, plus few languages/groups that cannot be clearly assigned to either subgroup. One of the latter, and the only one Ethnologue lists, is Yiddish, and its varieties. There is no need to create a "German" subgroup of High German so as to separate "Yiddish" from "German", which Ethnologue unnecessarily did. Despite being written in the Hebrew script, Yiddish is High German, and exhibits a mix of Middle and Upper German influences. There is no point to separate the other language groups of High German from it. A "High German, German" subgroup is just silly. Or else, if you had it, Yiddish was part of it, making it superfluous again. I hope, they straighten that with their next release.