Hi Marc
The design of the lab remains the same for each of the Vol 1 lab workbooks and the initial configs set up the base configuration for each of the Vol 1 lab workbooks. For example, if you load up the initial configs for Multicast you will notice that OSPF is configured for you along with VLANs, trunking, L3 links etc. If you load the BGP initial configs you will find EIGRP is configured on devices and you will configure BGP over the IGP. BB1, 2 & 3 run BGP & IGP's and depending on the workbook you are using at the time you may configure EIGRP redistribution, BGP peers or RIP redistribution etc.
The initial configuration files are the starting point for each of the Vol 1 workbooks. After a few sessions with the routers & switches you will soon start to pick up device IP addresses, physical links uses, IGPs running etc. I often print out the Vol 1 diagram and draw all over it during individual tasks (especially the BGP tasks).
I hope I have helped you.