That is not plausible IMO. Nobody has capacity to read the works of a miriad of nameless scientists, not even Isaac Newton. Even less likely that Newton and Leibnitz were both familiar with the same works of minor scientists.
What is much more likely, is that well-known works of other great mathematicians prepared the foundation for both to reach similar results
It gets condensed over time. Take for example Continental Drift/Plate Tectonics theory. One day Alfred Wegener saw the coasts of West Africa and East South America were almost a perfect fit, and connected the dots. But he had no need to read the work of the many surveyors that braved unknown areas and mapped the coasts of both continents in the previous 4-5 centuries, nautical mile by nautical mile, with the help of positional astronomy. The knowledge was slowly integrated, cross checked and recorded by cartographers. Alfred Wegener insight happened at the end of a long cognitive funnel.
One of the ongoing practices of science is people putting out summaries of the state of different parts of fields of work (and reviews of reviews etc.)