What the codes mean
Camelot notation places twelve minor keys on the A ring and twelve major keys on the B ring. A minor is 8A; C major, its relative major, is 8B. The numbers make common harmonic moves easier to spot.
It is a map of tonal relationships, not an analysis of the whole arrangement.
The four useful first moves
Stay on the same code for the most stable blend. Move one number with the same letter for a neighboring key. Switch A to B on the same number for relative major/minor. More adventurous energy moves can work, but should be auditioned carefully.
For mashups, a stable relationship is especially helpful when melodic material from both sources plays at once.
Why correct tags still fail
Key-detection services can disagree, especially with modal music, key changes, detuned recordings or tracks dominated by percussion. A tag can also be correct while one sampled section centers on a different chord.
Treat a detected key as a hypothesis. Loop the exact sections you intend to combine.