Parece que, começando no Vista, o número padrão de impressoras publicadas é de 20 impressoras.
Aqui está um resumo rápido e um link para informações sobre ele :
Printer Number Limitation related Policies
Click Start icon, then select Run...
Type gpedit.msc and press Enter. Click Continue if receiving UAC prompt.
Locate to two GPOs: Computer Configuration -> Administrative Templates -> Printers -> Add Printer wizard - Network scan page (Managed network) and Network scan page (Unmanaged network).
Double-click to change the configurations.
The AD-based Network Search in Managed Network
If wizard of adding network printer detects that the machine is on a managed network and the user is authenticated against the AD server it will attempt to do the following searches:
It queries the AD for printers. This works similarly to the Find Printers dialog in that it uses the same code to determine the user’s location and tries to find printers in the user’s location. It is different from the Find Printers dialog in that it uses the GC to query for printers instead of “Entire Network”.
The net search page will only show the first 20 AD printers it finds by default. If there are more than 20 printers that meet the location parameter on the query the search will simply return the first 20 that AD happens to return—this is effectively random in my experience.
The Location Parameters
Click Start icon, then select Run...
Type gpedit.msc and press Enter. Click Continue if receiving UAC prompt.
Locate to two GPOs: Computer Configuration -> Administrative Templates -> Printers -> Computer Location and Pre-populate printer search location text.