All the spillover should currently be going to EB3 ROW. The reason behind this is if a non-retro country like Nepal cannot get visa numbers though it hasn't reached 7% limit in EB3, retro countries like India cannot go over their 7% annual limit in any EB category. So, until EB3 ROW becomes current, there won't be any horizontal spill over i.e., no additional visas for retro EB2/EB3 i.e., have to live with 2800 annual visa limit per category. When number of H1Bs ranged from 65k to 195K before 2003 where majority consumed by India/China, and assuming even 25% of them applied for immigration and also considering GC filed by L1s and 2.1 visa usage ratio (spouses & dependents), it won't be difficult to predict the demand.
I think the main confusion comes from the false assumption that 7% limit is applied on all 140K visas and India 'always' gets around 9800 visas and unused EB1 for india goes to EB2 and so on i.e., vertical spill-over.
1. Unused EB1 pool on the whole first goes to EB2 pool.
2. The numbers would be given if a country in EB2 cannot get visas even if it hasn't reached its 7% limit. This is not likely as there will be lot of unused visas in EB2 also.
3. Unused EB1+EB2 goes to EB3 pool and gets distributed among the countries that cannot get visas though they haven't reached 7% limit. Since EB3 ROW is also retrogressed, everything gets consumed here.