It's inferred. Class A starport can build starships. Starships are built in a certain time as determined by hulls. It follows if you can't build a starship in that time frame you don't get a Class A rating. Note (iirc) that (somewhere it's mentioned, HG?) any world can build starships and spacecraft for it's own defense up to it's TL regardless of starport class. The starport class is for commercial purposes more than anything.
It may or may not be implied in LBB 2 (too etheral an issue to debate), but LBB5:High Guard states:
page19 said:… A planetary navy may procure ships at any shipyard within the borders of its subsector; alternatively, a planetary navy may construct ships on it s planet, using local resources, even if a shipyard is not present.
Construction Times: Ships of 5,000 tons or less can be completed in 36 months or less by any competent shipyard. Ships over 5,000 tons require from 24 to 60 months to complete, based on conditions, volume of orders, and the degree of haste desired by the ordering government.
So building 1 scout in 35 months would meet the stated requirement.
Starport classes (IMHO) appear to be based first and foremost on what they can do. How soon the starport shipyard can get around to your repairs and how long those repairs will take is for the referee to decide based on his/her vision and campaign. ... The alternative, is that every class D starport may actually be Class A but too small to meet the ISS production criteria. That makes the ISS ratings virtually useless.
[EDIT: I just threw in the planetary navy part because you mentioned seeing it somewhere in HG and it was on pg 19.]
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