Many involved in group multiplication have told me most groups have a limited lifespan for multiplying new groups.
If one group is going to help start another group, it usually happens in the first 1 to 2 years, with steadily decreasing odds of multiplication in years 3 and 4.
This is testable by collecting data on your groups: when was each group formed? What groups formed out of them? When? Then compare the dates.
If it is broadly true (and it is holding up true so far in big movements and small), it would leads to two theories about what we should do:
1. Allowing, endorsing, supporting, enabling, persuading early group multiplication is critical. If you make people go through a 4 year course before allowing their groups to multiply, odds are they won't. You could be killing a movement before it even starts.
2. If the movement is stalled, going to existing people and asking them to multiply may not work at all. The emphasis should rather be on seeding brand new groups (or starting a brand new planting). You need people with an apostolic gifting to do this.