TLDR of the logic behind that sum for anyone else who wondered like I did:
They claim the ship's value before the crash as $90M, and that estimated costs for salvage and repairs to the ship are $19.5M and $28M respectively, leaving the value of the ship now at $42.5M (points 15-17 in the main document).
They then add the value of pending freight ($1.17M): "Petitioners offer an Interim Stipulation
of Value in the amount of $43,670,000 (i.e., sound value of the vessel plus pending freight less
repair costs and salvage costs)." and mention that they'll file updated numbers once salvage and repair costs are confirmed rather than estimates.
IANAL nor in the US, so I'm curious whether this is standard law to be able to limit your liability to the (post-crash) value of the ship and the only thing in question is how the numbers end up, or if it's a long-shot hope that the companies' lawyers figured they might as well try asking for in case a judge feels friendly?