Which one should I use in a sentence such as this:
The abstract or the references information of many papers was/were not available.
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The noun "information", like the nouns news, money, advice, etc., is uncountable and is used with verbs in the singular form no matter what modifiers are used with it.
If you use countable nouns, in the subject-verb agreement it doesn't matter what comes between the subject and the verb. The verb agrees with the subject, not with a noun or pronoun in the phrase.
One of the boxes is open
The people who listen to that music are few.
The team captain, as well as his players, is anxious.
In this regard, don't let "of many papers" in your sentence mislead you.
Whether the "abstract information" or "references information" collocations are appropriate usage, is another question.