There are certainly more than 3 B-24s between 44-51537 and 44-51784. Actually they were probably all built. They have no entry in Mr Baugher's website possibly because he had no data on them or had not treated it yet. These lists are manually made from a variety of sources by Joe Baugher himself.
For example:
44-51540 was damaged in an accident in France in November 1945 (
http://www.aviationarchaeology.com/s...515&Submit4=Go, also listing 44-51558, 44-51559, 44-51561 and 44-51580 just for the serials beginning with 44-515, all with repairable damage)
44-51562 was lost in the Pacific on 14 September 1945 (
http://www.questmasters.us/William_A_Biergel.html). So the final fate here is known but not on Mr Baugher's website either.
As for finding information on the date they were sent RFC I have no idea, but you can contact Joe via his website and he replied quickly to me some years ago.