You've got a good handle on the situation.
If you're collectively talking about each symbol's individual specific meaning, use the plural. The group is the collection of interpretations, and individual interpretations may correspond to different symbols.
If you're talking about the property of having an interpretation or if many symbols combine to form a single aggregate interpretation, use the singular. The group is the collection of symbols, and they all have some kind of interpretation.
If you're unsure which one to use, try removing of the symbols from the sentence. The grammar will be the same without it, because it's a prepositional phrase functioning as an adjective to describe interpretation[s]. The fact that symbols is plural doesn't make any difference to the verb.
The interpretations [of the symbols] follow those described above.
Each symbol has its own, possibly different, interpretation as described above.
The interpretation [of the symbols] is unique.
Multiple symbols combine together to form a single unique interpretation.
An interpretation [of the symbols] is always possible.
A symbol always has an interpretation, but the interpretations may be different for different symbols.
Both are understandable.
I've mostly heard the following used:
Is the girl coming or are the boys?
Are the boys coming or is the girl?
An implicit difference is in emphasis, the more preferred of the options would be mentioned first, i.e. preference for the girl showing up :
Is the girl coming or the boys?
Best Answer
Answer: either form is fine.
Data is typically treated in contemporary English as a "mass noun", an undifferentiated collection (like "sand") that takes the singular "is".
This is the most common usage today.
But it CAN also be treated as a plural of "datum" and take "are" with equal ease and correctness.
If we recast the sentence with an explicit plural noun: "In this section you can make a payment: verify carefully that all the answers submitted ARE correct and confirm by clicking the Proceed button." then you must use "are".
If there was prior discussion of "data items" or the like, then the established context may cause the plural treatment to be preferred for continuity.