“Rez-de-chaussée” and “pas spécifié” are correct translations.

Parterre has very specific meanings in French.
And “ne pas spécifié” is not grammatical and moreover could be mistaken for “ne pas spécifier” which is an injunction and not a piece of (non) information.

In this case the dictionnary is right, “rez-de-chaussée” (with an ‘e’ at the end) is a better translation than parterre which means a part of a garden with an aesthetic purpose.

“Pas spécifié” is not good french, when there is no data we would most likely say : “non spécifié”.

You have 3 questions here.

• Floor 0 is “rez-de-chaussée” in French (at least the way it’s spoken in France).

• “Pas spécifié” is acceptable to a degree in spoken French, not so much in written French, “non spécifié” would be better.

• “Pas” or “ne pas“. Again, that’s a verbal ellipsis. Ne should always be there, but in spoken French, it often disappears. This can lead to ambiguity.

Originally, ne is what makes the negation. The etymology of “pas” and “jamais” are exactly the opposite of their current meaning because of this. The only remainder (and cause of ambiguity is “plus”). There is a direct parallel with not and ever/more in English.

For example, “Je (ne) mange jamais de bonbons” (“ne” is rarely used in speech) would mean “I (n)ever eat sweets.”. No one today would understand jamais in this context to mean ever or always: it’s always understood as never. However, there are cases where the “ever” meaning is still used. For example: “Il court plus vite que jamais.” (More than ever).

I’m not aware of any similar example with “pas” (although my understanding is that it comes from similar Latin roots and constructs).

There is still an ambiguity when you say “J’ai plus de bonbons.“

• If you pronounce “plusse”, it’s meant as it’s written (“I have more sweets.”)
• If you pronounce “plu”, ne is implied and should be written “Je n’ai plus de bonbons.” (i.e. no more).