The checks from Bosch state, "By endorsing and depositing this check, I acknowledge the individual release of Claims set forth in the Bosch Settlement."
If Bosch actually is splitting the payments into two installments, then they should not have this statement on the checks (Because you're still entitled to receive the other half)
I also find no where in the Bosch settlement that allows them to wait to pay 50% until after emissions modification.
Owners of vehicles with no eligible previous owner should receive a check for the full amount stated in the BOSCH Settlement.
Although there is no provision for Bosch to withhold 50% of the compensation until a later date, they have no deadline, so they may be holding off on the full amount until they can confirm the absence of an eligible seller.
I don't think the 50% payments from Bosch have anything to do with the emissions modification.