Did Nortia and Fortuna represent the same thing?
Later associations between the two goddesses do not justify treating them as interchangeable. The kind and extent of surviving evidence are dramatically different.
First tradition
Nortia is recorded in Roman literary testimony in connection with a nail ritual at Volsinii, where nails reportedly marked the passage of years. The report is narrow and leaves much of her cult unknown.
Second tradition
Fortuna has a much broader surviving visual and textual record, including sanctuaries and representations with the rudder and cornucopia. Her cult titles differed across places and communities.
How to compare responsibly
Compare the evidence category before the modern interpretation: a later literary passage about an Etruscan ritual is not equivalent to a surviving Roman image.