Unlike the official toponymy approved by regional decree, which went through a peer-review of a toponymy committee, of the municipal council and of the autonomous region, there is no guarantee that the same happened to those two documents. I suppose it could be an alt_name or old_name candidate, since we don't know if that was the name previously used prior to the adoption of 11 december 2012 regional decree n. 464., but it is possible it is simply a mistake that keeps on perpetuating itself. And as the municipality of Sarre itself reminds the reader on its website:
https://www.comune.sarre.ao.it/il-paese-e-le-associazioni/paese/frazioni/
"Lein".

Now, I do have to thank you for mentioning the alt_name_1 tag, which I have used for Champdepraz, where the regional decree mentions both the official name and alternative names: https://www.regione.vda.it/enti_locali/documento_i.asp?pk_documenti=1181

But in the case of the municipality of Sarre, no alternative names were provided. Therefore, I cannot recommend Leyn as an alt_name or old_name.

Following your comments I will, however, review previous edits of mine to make sure that when a municipality has established "alternative/in-use names", that they are reflected in the tags of the locality/hamlet/village too. Of course, those cannot supersede the official name, by definition.

Does this answer your concern with respect to this particular village?
