So credible people telling similar stories over long periods of time does not constitute evidence?
I'm afraid not.
Years and years of UFO accounts doesn't add up to an alien invasion.
The Abduction accounts don't suggest we need an advanced alarm system to catch when the aliens enter our homes.
At nost these accounts make for an opportunity to study the Psychology and sociology of the human tendancy to create such things.
On the other hand:
For many years the Government of Singapore insisted that there were no cobras on the Island of Singapore. Countless people got bitten and had to go up to JB in Maylasia forb the antivenom that wasn't availible in Singapore for above reason. All these accounts of cobra biites where chalked up to anecdote.
Eventually with the capture of a cobra, the official position was altered and Singapore hospitals began to stock the antivenom.
Heresay and anecdotal reports may not measure up to the desirable level of evidence, but they do give a warrant for investigation.