Most intellectual processes take place according to the rule of Trial and Error.
It is only natural that reasoning and research leave temporary doubts, shadow zones, hypothetical statements, or unproven accounts. Also, cultural advancements must sometimes risk errors and missteps in hope for future amendments and correct answers. We could even allow for certain "inventions" or "fantasies" to cover unresolved stages in order to yield a more compact explanation.
If this is true for intellectual progression in general, it is obviously so also for social science analysis and in particular for the realm we are here interested in, that is: Research on History of Music.
But the Trial and Error approach should establish certain limits for inaccuracies beyond which the investigation cannot be considered as closed, culminated or acceptable. It is not a matter of universally established fixed or rigid limits,. On the contrary. The amount and level of errors an investigation can bear depend on the investigation itself as a component of its inner credibility. This at the same time depends on many factors, such as the way it is presented, its scope, the intellectual probity displayed, the documentary apparatus provided, and so on.
No objective or general rules can be given to assess whether a History of Music account (or any other kind of social science account) has infringed the acceptable limits of errors and unproven "truths". Nonetheless, the reader can "sense" the degree of its credibility, and discard or accept its contents as a whole, no matter how many errors or foggy statements can be detected.
We are obviously in the realm of subjective appraisal, but when this appraisal is shared by most readers or by a great amount of readers, we can conclude there is a swing from subjectivity to undeniable objectivity. And this is the case with the traditional historiographical line about Luigi Boccherini. Few important musicians have been hit with so many Errors, Myths and Legends as the great cellist and composer from Lucca.