The generated base register is zero which is significant. From the incomplete fragment shown, it looks as if the label has accidentally been defined in low storage at location X'00A0', in which case the generated code is correct.
However, a missing base register could also result from a known HLASM problem fixed a couple of years ago. If the target is invalid or out of range, there should be an error message, usually ASMA034E, but there were cases in which the usual check failed if it was too far out of range, fixed by APAR PH52834: https://www.ibm.com/support/pages/apar/PH52834 Note also that BCTG does not support 20-bit addressing if OPTABLE(ZOP) or OPTABLE(ZS1) is specified, as the initial implementation only supported 12-bit addressing. Jonathan Scott
