We have the below DEFINE code to set Primary and Secondary space if the primary/secondary exceeds 5800 CYL for Non extended datasets (DC - Extended Addressability = NO)
DIF fails to reduce the Primary space if the space is larger than 64200 cyl and ended with JCL error but it could successfully reduce it's primary allocation if the requested space is less than 64200 Cyl.
DTS was reducing primary space allocation successfully if it was exceeded by 75k CYLS
Evidently the code adds a certain amount to the allocation to consider for an INDEX component. For this allocation, the primary data component amount was 65000 cylinders.
When the code added an estimate of the index component, the total amount went to 66301 cylinders, which evidently is more than can be stored in a half-word.
This leads to the DIF/RTF failure.
But the ASR could set the DATA component lower in the DEFINE environment and avoid the problem as circumvention.