No one list of Loyalists can be considered "the" List. There is no simple definitive and accurate list. You must consult them all, from the Old UEL list to Reid's book The Loyalists in Ontario: The Sons & Daughters of the American Loyalists to all the variant lists made.
Reid's book on Loyalists was never intended to be the Bible of Loyalist families. Reid simply organized index cards into what he thought were family groups. *Many*
if not most families are incomplete. Some individuals are incorrectly placed.
Reid's book is a wonderful resource, and a great starting point for your Loyalist research, but you should verify independently that a child he places in a family group does belong there (by looking up ALL petitions for that family), and never never assume that because an individual isn't in the family group he/she doesn't exist or isn't a Loyalist.
After 1796 the Executive Council kept a list of Loyalists based on District Rolls. This became the Executive Council UE List and contains about 3,500 names. It is not considered a complete list, but it is considered more accurate than the Crown Lands (Old UEL) list.
The Crown Lands Dept. created a second list, based on other records. This became the Old UEL List and contains approximately 6,000 names, but not all qualified.
When searching Loyalists you also need to consult pay lists, muster rolls, and the land records. For a good reference to what is available, see Brenda Dougall Merriman's book "Genealogy in Ontario: Searching the Records" Look under the chapter on Loyalists.
Check out this list of Loyalist Books & Resources which will help you find your Loyalist ancestor