Question

when data has been on data is a dash​

Answer 1

$\huge{ \underline{ \bold{ᴀɴsᴡᴇʀ....{ \heartsuit}}}}$

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.