4t2b:
The difference is that BA has no obligation to "publish" its offer. They can do so if they feel that it is to their benefit but their offer is not determinate on any other individual or groups' approval.
From what I understand Unite/BASSA have the offer in hand, have been issuing repeated commentary to their membership about their recommendations regarding the offer, but they still haven't submitted it to their membership for consideration.
Why the delay? I realize that the more militant membership will vote against the offer regardless of its content, but many members will want the opportunity to consider this offer and weigh the positives and negatives to themselves personally. This will be a serious decision for many individuals.