Generally speaking when you start to look for books on paganism one of the first pieces of advice you might get is to avoid things published prior to and during the Victorian era*, or books that rely too much on these as sources. Generally speaking this is good advice as this period was a time when scholarship was heavy on unsupported supposition and opinion and short on factual evidence. There is however one large exception to this general rule that I'd like to address today because its an important one, especially for those who have an interest in fairylore.
There was a movement during this same time period for folklorists and anthropologists to begin collecting the stories of the people, both the old folk tales that had been passed on for generations and also stories of personal experiences and family lore. The motives for doing so were likely less than ideal in some cases but the result is a multitude of books that are full of stories which relate people's first or second hand experiences with the Good Neighbors and the complex of beliefs surrounding them over the last several hundred years. For modern people, especially those interested in the Fairy Faith as a viable system these stories are vital. While the usual rule of thumb may be to avoid books dated prior to the mid 1900's or so when we are looking at books of folklore the rules are different. Although I still advocate being careful with anything sold as 're-tellings' because those usually involve a lot of fictitious additions and translations because they often alter material in the translating there are many important folklore collections to be found from the 1800's.
Of course when we read these stories we must still be cautious to watch for the editor's influence on them. It is usually easy to tell where the person writing them down has inserted their own opinions into the narrative or where they have simply written down exactly what they were told as it was told to them. In many cases we get a mixed result where there may be a great deal of wonderful anecdotal information preserved, but we must pick through secondary opinions to get to it. We see this with the Fairy Faith in Celtic Countries, which espouses some popular theories of its time that should not be trusted now - like the fairies as native British pygmies - while also giving us some valuable folklore. We shouldn't throw out the baby with the bathwater, but rather learn the discernment to judge what is valuable and what is just some Victorian academic's personal opinion.
We also need to keep in mind something else. Anecdotal evidence is not limited to a hundred years ago - it still exists today. We have the strangest habit as a culture (speaking especially of Americans here) of giving some credit to people a hundred years ago for actually possibly having had some genuine experience of the Otherworld while simultaneously doing everything possible to rationalize away people in our time saying the same things. We can believe that a hundred years ago someone saw or experienced Fairy, but simultaneously believe that no one can really have those same experiences today except intangibly in dreams or meditations. And yet people do still see and experience Fairy as they always have; we are just more reluctant to talk about it today because of the strength of the disbelief. Not to say we should immediately believe every claim by every person, because discernment is always valuable, under any circumstances, but I'd caution against deciding that our own cynicism should be the measure for everyone. What we personally see or understand is not the limit or ability of everyone else. It may be best to find a balance between a healthy skepticism and an attitude that espouses, as Shakespeare said that 'there are more things on Heaven and earth than are dreamt of in your philosophy'. There have been some efforts to collect modern anecdotes, such as 'Seeing Fairies' by Marjorie Johnson and Simon Young as well as an excellent documentary 'The Fairy Faith - In Search of Fairies'. These modern collections re just as important as the older ones because they show that the beliefs are still vital and alive, if less visible.
Ultimately anecdotal evidence is important because it gives us a snapshot of the beliefs of the people at different points of time. It shows us not only what they believed but in practical terms how they felt the different worlds interacted and effected each other. Reading a range of anecdotal evidence across different periods of time is important, and for those interested in fairylore its essential to see the beliefs in different areas and the changes to beliefs over time. We can learn a great deal from this material, if we are willing to embrace the older as well as the new.
*with the exception of much older manuscripts, particularly myths