A bit of history...
In CT, MT, and T20, ship receipts were in the following pattern for merchant, lab ship, corsair, and yacht
1st: Down payment made, 40 years owed
2nd-4th: 10 years payments made each
The Type S was simply a ship permanently assigned to the scout, and only one, no matter how many receipts.
In TNE, the concept of ship shares was introduced. You then rolled for the modifier for ship type based upon total party shares. Which gave a modifier to rolling for what kind of ship was received, based upon the category of the largest pool of shares.
Was really cool, and really a pain.
The ship share concept was migrated in, but changed by Gareth to a cash value. The problem was, people wanted to cash them in for cash...
The ship share concept was a simplification, but one designed to keep players always saddled with a mortgage... unless they stayed entirely within budget.
Note that a Scout share would be 100% of a scout if we want CT/MT equivalent... after 50% discount for guaranteed age (40+), that's MCr15
A Type A is around MCr40, and 5 receipts, so a share would be about MCr8.
A Type L is around MCr140, and 5 receipts, so a share would be about MCr28...
A Type K (Safari) is around MCr70, and 5 receipts... making a share about MCr14.
If we say, "Whichever kind has the most shares is the base type, other types' shares count as half the majority type's value" we can get the flexibility of TNE without the dual tables...
And add that every 20% of total price not paid is 10 years owed...