Does trading ability time limit stack?

Does the time limit on the SS trading ablility stack?

e.g.
If I buy a $5 SS package then I decide to three days later buy a $10 SS package do I then have:

a) Just the $10 270 days trading ability
or
b) 100 days from the $5, + 240 days from the $10 - the 3 day gap = 337 Days

The donation page says:
"The game remembers the best package you have bought. If you bought the VIP package you will not lose permanent trading if you buy another Ultimate package later."

Which doesn't really answer this question fully, but sort of implies a)

-Alex

b)

Thank you for the quick reply.

-Alex