The FHL catalogue describes this as "Alphabetically arranged lists of births, marriages, and deaths from the early 1800s to 1930."
In reality, the number of records prior to about 1875 is small. There are some but finding records before 1875 is more the exception than the rule. For a family I was researching, father born 1815, died 1895, married twice and had several children born in Gray, I only found the second marriage and the death.
The preface says "This compilation is meant as a guide to the vital records of Gray, Maine. As there may be errors or omissions in this work, original records should be used as a source for research. The death records list place of birth if known."
It does not appear to me to be a literal transcription of the records, but I have not seen the originals.
Beyond this short preface, there is absolutely no explanation of what the scope of this book is, what it is based on, how records were selected, what protocols regarding spelling, etc. were followed. One can only guess why the early records seem so under-represented.
In marriages, each couple's full entry is listed once, sometimes under the wife's maiden name, sometimes under the husband's name. The other spouse will direct you to the spouse with the full entry. For example, Alvin Skillin's entry says "See Libby, Lucy". The only problem is that Lucy's marriage is arranged by date within her surname (Libby is a separately ordered list from Libbey, and Skillin, Skilling, and Skillings are each independently ordered lists), so you must flip through a couple of pages of Libby marriages if you don't happen to already know the date of Lucy and Alvin's marriage. --Jrich 21:18, 10 September 2009 (EDT)
Other sources of vital records of Gray from the Family History Library Catalog are all transcribed records, but may have better sourcing. See: