The expected algorithm below, based on the shell script pack_maker.sh from swupd-server, is: 1. parse the latest Manifest.MoM, 2. extract "previous", 3. parse the "previous" Manifest.MoM 4. repeat the steps 2-4 $SWUPD_N_DELTAPACK - 1 times. This enhancement is useful because there might be correcting releases whose version id is not a multiple of 10.
Right now there is no algorithm at all anymore, the versions against which deltas are to be calculated have to be set in SWUPD_DELTAPACK_VERSIONS. Not sure whether this is really required at the moment.
Upstream swupd has changed a lot and integration with the Yocto Project would be tricky and need rework to the layer. Closing this as obsolete since any new integration would need rework and have its own issues.