A large number of in scope employees in GTS will be on enhanced redundancy terms as part of the TUPE conditions. These conditions are voided should you volunteer. and you have to accept the statutory terms.
Every case is personal and different but I can't believe the numbers would increase that much.
The cynic in me believes IBM are looking for as many people as possible to "fall on the sword" to keep the payoff costs down to a minimum by ticking people off by reopening the EOI.
This to me sounds like desperation.