sdoebler, you may be right, but this is a direct quote (with emphases added) from the arbiter website:
"A 'firm' block is one that your assigner cannot override when making assignments. Normally, an assigner can still make an assignment even if you have a date blocked. They simply are notified that you’ve set a block, but they can still assign you. Marking blocks as firm prevents your assigner from overriding a blocked date or time."
I only learned about firming blocks after several years of being on arbiter. Mark, is Junior aware of this capability?