Personally, I think it's kind of confusing making ship cargo limits on tags. It feels like it would be a whole lot better to drop ship cargo limits entirely and just make ship class/type restrictions and then sub-restrictions with the limits based on the origin of the ship.
Examples: The Pilgrim Liner is good for basically all of Sirius, including freelancers, even with 4,300 cargo, but pirate ships like Liberty Rogue and Outcast ships are not acceptable for Freelancers, because they are Liberty Rogue and Outcast exclusives. Similarly, company ships could be exclusive to company faction members, or people with their tags, so then a freelancer could have an advanced train, because that's their only choice for a 5k.