Thanks for all the input.
OK, so ND should be reserved for coins minted without a date as a design choice. Agreed, makes sense.
As for the “?” option that was replaecd with “undetermined” as a general notation, well, I think that's accurate for many issues where the coin is worn or damaged and the date is unreadable, and it's technically accurate for worn buffalos too, but that's not the vernacular!
Dateless buffalos are a special case that deserve special notation: DATELESS.
I've been collecting coins for about a thousands years now and as you might all agree, dateless buffalos are very common.
In fact, they're so common that everybody who collects US coins has som dateless buffalos and we all call them dateless.
So, for buffalos, where dateless coins are common, normal, frequent, bought, sold, and traded by the bag, and everyone in the hobby calls them “dateless”, I think “dateless” is a prefectly fine option to place under the date column on Numista. I'd also include a comment noting the frequency of dateless buffalos, the cause, and value. It's a very minor change, wouldn't take more than a swift update, and would make immediate sense to all new and existing members.
Thoughts?