Do you have Edward's birth record yet, or the records of either of Lucy's two known marriages?
There appears to be an unnamed Luscombe chiild registered 1899q3 in Dublin North, ref 2, 488 which could be him.
Also, a John Luscombe married in 1898q3 in Dublin North, ref 2, 471 and a Lucy Lane appears with the same reference.
Similarly, a Lucy Luscombe and a Thomas Guilfoyle both married in 1914q3 in Dublin North, with the same reference of 2, 496.
If these are your family there might be further details of previous names, or other evidence to suggest what is the correct infomation.
A point to note is that several birth records that I have obtained from GRO Ireland have had a surprise mother's maiden name on them. Other evidence such as addresses and father's occupation have shown that it is the correct record. I can only assume that, perhaps with a screaming child in the room, the registrar has made an error or maybe the mother was too distracted to give the correct details.
Also, in many cases the child was registered by someone "present at the birth" who may have confused the details of several infants being registered at the same time.