Could we use the ablative case alone to signify the "from" parts?
i.e., Nōn Germaniā, sed Italiā venīmus.
Is this correct too?
You generally use the ablative with a preposition in Latin.
My understanding is that that's only used with cities and towns, and certain idioms where the ab-lative still has the sense of "carried away from":
Isn't 'a' just a short version of "ab"? If so, "a" before "Italia" is currently considered a typo.
ab before words that begin in a vowel (Italia), a before words that don't (Germania). It should even be marked as an incorrect answer, not just a typo in my opinion.
Marking as incorrect would make it easier to learn that it's wrong.
Yes, but it's impossible to make. Because it depends on Duolingo software engineers, not from course contributors, they only add some contents, don't change the software.
"Nos a Germania non venimus, sed ab Italia" is accepted. I can see how loose the word order is.
What an awkward way after saying it.