IMO starports that have Class A or B or C facilities will still be rated lower if they don't have the capacity to service all their traffic properly. I've used that idea to explain Class D starports on stellar-tech, high-population worlds a couple of times already (Rethe/Regina[*] and Forine/District 268[**]). I expect to use it again in the future.[A starport definition] is just given in abilities, but doesn't say anything about capacity. How do you define a starport that has class A facilities but couldn't really service more than a couple ships at that level at a time? Does it matter if that's as many ships it's likely to see at a time?
Hans
[*] "At one point visiting starships could not expect to get any service at all, at least not in a timely manner. Things are improving now and the starport will soon be reclassified to Class III and eventually back to its original Class IV status."
[**]Forine's starport would be Class A if it wasn't too small for the traffic it has to handle. As it is, casual visiting ships cannot be sure of getting even elemetary service in reasonable time, reducing its official class to D. This state of affairs has been chronic since 1104, when a construction workers' strike resulted in riots and extensive destruction of starport facilities. Every attempt to solve the conflict and remedy them since then has proved a temporary stopgap at best.