How does the topic you research even become a topic worthy of research and review? This is part of the Information Cycle. The amount of material you may find on a topic is related to where the topic falls within that cycle. The type of information you find also depends on where it falls in the cycle. Is there enough information on your topic? It depends on the information cycle.
From the University of California San Diego
Timeline of Information Cycle: Minutes and hours after an event you will find basic information such as who, what, where, whey and when. Television and websites would have this information. If the story lasts several days the media may continue coverage, adding details and presenting expert opinions on the event.
Weeks after coverage would include basic analysis, causes, opinions and editorial bias. Months afterwards, information moves beyond media outlets and may be found in academic publications featuring analysis, biographies, and theories.
Years later books will contain bibliographies, background information and critiques of previous coverage and analyses. After many years, information may be found in print and online in encyclopedias, databases, textbooks, etc.
While the information cycle moves in a linear way, when you research you may choose to start at any point in the cycle depending on which type of information you want. If you want interviews from close to when the event occurred, newspapers, whether online or in print are a good choice. If you want a basic overview of the event, an encyclopedia works well.