the amount of cargo of my Cobra Mk. IV OXP is being shown as "45", but it should actually be "45 (+15)"
This is a limitation on what information I can access at runtime. The default amount of extra cargo (if none is specified in shipdata.plist) is 15. However, that setting only comes into play if the ship has an option for a large cargo bay specified in shipyard.plist. I can't read details from shipyard.plist at runtime, which means all I have access to is the shipdata.plist file, which means if no extra cargo is specified there, it's hard to assume it's actually allowed.
There are two ways around this. First, you could specify the extra cargo in your shipdata.plist file - if it's specifically set, I can assume it's correct.
Alternatively, I have a list of exceptions inside Ship Comparisons which controls the two settings I can't read from shipyard.plist: large cargo bay, and weapon facings. For future reference (and I'll put this on the wiki page as well), to override these values you can do this:
worldScripts.ShipComparison._extraData["Cobra Mark IV"] = [15, 15];
The ship name should be the generic name for the ship, rather than the shipkey (although if you have a specific variant of the generic you want to include you can do that as well), and the two numbers are "amount of extra cargo" and "weapon facings" (where 15 means all positions).
In any case, I've uploaded v1.8 of Ship Comparisons which add the Cobra Mark IV to the list of exceptions, so you don't need to do anything for this ship now.
Thanks for letting me know!