In an academic paper, while describing an organization being not the only example of its kind, I used a sentence like: This organization was not a one-off. However, I feel like it sounds too colloquial. Is there a better, more formal way to say it? Thank you...
Unique would seem to fit the bill.
Outlier may fit the context better:
"The organization was not an outlier"
What about "Organizaion XYZ is no freak of nature/chance; there are many more that belong to its tribe" or "Organization XYZ is only one exemplar of its type; there are many companies kindred to it"? I think this really depends on the context - you will have to decide whether it suits the discipline - social science, or management or other such .