SOURCEBOOK DOES NOT SAY WHAT OTHERS HAVE QUOTED IT ABOUT WEADOCK SURNAME (THAT I COULD FIND)
According to the “Book of Rights” ( translated by John O'Donovan), Mac Uadog Maddock was a member of the MacMurrogh family. Since he seemed to have lived in the early to mid 1600's, the (“Book of Rights, Index page 311 and text page 208), this is too late to use as a source that "knocks out" the possibility of a Lancaster marriage family connection. ( This family which ruled in the late 1300 to early 1400's.)
This not only doesn't answer for the Weadock name as a whole, it doesn't even answer for the surname of Uadog Maddock. That is, if he lived in the 1600's, especially.
MacMurrough is probably MacMurray today and not Vaddock or even Maddock. The Irish surname Murphy was also taken from MacMurrogh as far as I can find, but it is still not shown to be the base of Waddick, Weadock, etc.
I know that this source book was cited as for the origination of the Weadock surname. As far as what I could find,"The Book of Rights" did not specify this, it just said that Mac Uadog was named Maddock and was a member of the MacMurrogh family.
At such a late date (the 1600's as opposed to the 1100's when the MacMourrogh family was traced to) this name Maddock and Weadock could still have originated as others have suggested, with a marriage into the royal line of Henry (IV) Lancaster who lived from 1367 to 1413 and also plenty of time to have been connected at some family level to Henry V who lived from 1387 to 1422.
The Mac Morrough family was known for it's associations with Henry II for instance and a match to an English King's connected family (like a Belgian one) would not be totally unheard of.
From the notes that I have, from "O'Hart's Irish Pedigrees" Daval Mac Vaddock was an originator of this name was son of Henry V and lived in the mid 1500's.(O' Hart's Irish Pedigrees, Vol. 1, page 567).
Certaily the "Book of Rights" is a great source too. But I think it was misinterpreted (Index page 311 and text page 208 at least).