Fingerlings were stocked in the lower Letort. And wild trout are found in the lower Letort.
This does not prove that those wild trout resulted from the fingerling stockings.
Does anyone really believe that if no fingerlings had been stocked that the lower Letort would have been without wild trout?
If the upper part of a stream has a good wild trout population, and the lower part of the stream has conditions suitable for wild trout, it will soon develop a wild trout population. Trout move around.
This reminds me of when people were attributing the wild trout population in the Little Juniata River to fingerling stockings, when in fact there were wild brown trout there a long time before the fingerling stockings began.