Hmm interesting. I could have sworn i had 7 hundred something cargo slots in it last time i used it.
No... it was a year ago since you played the game, correct?
Here is what happened.
Lakon came up with an anti-thargoid combat ship... based on the Type-9. This ship is called Type 10 - Defender. When it came out, it turned out to be much better than the Type 9 transporter... same cargospace, but better on all aspects regarding weapons, hull and maneuverability.
So, FD decied to make Type 9 great again, by adding a second Class 8 slot; which now makes it very close to a Cutter, regarding cargospace.
EDIT: Essentially... there were no point in flying a Type 9, if they didn't add that change to it. And to be honest, it added a good balance to the cargoships. While a Cutter is way better than the Type 9 (not so much cargospace but all other aspects), it still makes the Cutter the best trading ship in the game, but it is nice to have a non-ranklocked alternative that can do similar deliveries.