Sam, the book 'Andreas' was written from the research done by Donald S Dugdale over many years, which he had deposited in the National Archive at the Manx Museum Library [MNH].
Only part of his research into Andreas places and families was included in the book, along with good maps and other details supplied by the editor.

If you are mainly interested in one place it might be worth asking the library for their fee to scan and send you that section from DSD's work lodged with them, which may be considerably more extensive than is included in the book. (Obviously I don't know this for sure - based only on the three places and families I have seen both in the book and in DSD's research held at the MM.)

The MM library staff may tell you to hire a local researcher, in which case ask them for the call number/shelf number for DSD's Andreas work. Or look when you can go over there yourself?

Sue