I might note that they apparently reversed themselves regarding evidence of abstinence program success to say...
I don't think there is neccessarily any discrepancy. Their initial statement was with regard to those taught through Abstinence only programs and the second with regard to those who had actively taken a public 'Virginity Pledge'. So an abstinence only eductation program does not appear to change the initiation of intercourse but taking part in a pledge scheme does. Perhaps those who take pledges are also those who would have waited longer before initiating intercourse anyway and all the pledge programs are doing is identifying a more abstinent subset of the teenage population.
TTFN,
WK