They can be - but there have been many nde experiences that have elements that do not fall under the scientific definition of anecdotal evidence. For example, there are quite a few reports of nde experiences within a hospital setting where the individual describes events that took place during the time they were pronounced dead and often times from a different perspective than their physical body - with these events being corroborated by multiple individuals that were in the room at that time. My understanding is that these do not fit the definition of anecdotal.
Such phenomena do not necessarily support the notion of life after death but they are evidence of consciousness having a non-local capability with reference to the physical body. They also show that this non-local consciousness has the ability to see - though not with a physical eye. It is a very sticky problem for the materialists.