Hold-up with contract

I received and accepted a verbal job offer with Tier 2 IB about a month ago and have since provided all my background docs to HR and completed a mandatory psychometric test. Have been waiting for them to produce the contract and the latest feedback is that all the approvals have been completed out of the region and they have the headcount, but some very senior people at HQ-level still need to go into the system and complete the approval. I've heard that this bank moves quite slowly, so no reason to doubt the story. But as we're into Q4, I'm getting concerned about the possibility of a headcount freeze or some other obstacle screwing things up for me.

I have been approached a couple times by headhunters about other (less appealing) roles and didn't show much interest, but perhaps I should not assume that I have a "bird in the hand." Is this situation within the normal range of people's experience?