Douglas did not include "hok-ló" in the main text. The hok-ló he quoted was about the name applied to people in Swatow (Shantou) and neighboring regions by others in Guangdong back then.
I herein include snapshots from The Chinese Repository I mentioned. I usually download the .djvu format and then search for the keywords I want. I used google with the search strings of "hoklo site:archive.org" and "hok lo site:archive.org" to find books that contain hoklo or hok lo first. Then download those relevant books for further reference.
Of all the books I downloaded from Internet Archive with references to "hok-lo", George MacKay (馬偕) was the first one to use it to clearly refer to Minnan-speaking people in Taiwan in his book From Far Formosa of 1895, the year Taiwan was yielded to Japan by the Treaty of Shimonoseki (馬關條約). Another book called Pioneering in Formosa by W. Pickering (必麒麟) in 1897 also said the same thing. There's an earlier book of 1884 by the name of "The Children of China" that seems to use hok-lo to refer to people in Fujian. But it may just refer to people around Shantou.
Snapshots from three books are included here first. Those from other books will be posted later.