If you read the jacket of the u2.com version, Terry Lawless is credited for "Pride", which isn't on the CD.... at some point, an alternate, longer track listing was prepared and mixed : however it was then edited to the 15 track CD. Also, if you listen to the finished audio mixes of the download songs, they aren't finished masters (the volume/EQ and production isn't quite as polished as the CD), so they probably created
a) final mixes of the 20+ songs originally intended for this record
b) edited down to 15 songs and created a finished CD master with new EQ
Primarily, if you want to splice the download songs back in, be prepared for a quality drop and some brutal edits unless you go in and blend the tracks across each other.