If you want to listen ONLY to the IDs you programmed in (closed option), then you must disable the wildcard. You can do this by locking it out, deleting it, or editing it to change it from wildcard to an actual ID. Don't worry, because you can always use the DUP function and make another wildcard whenever you want. (I have done it all three ways, but I now prefer to just lock it out and keep it handy.)
If you want to hear all active IDs, including the ones you programmed in with your text tags, you must keep a wildcard unlocked (open option). This is a good way to find new IDs, or to check on what you are missing by hearing only your programmed IDs. You can simply go to your wildcard and unlock it from time to time to do this, and then lock it back whenever you want.
No, sorry my explanation was confusing, and it has nothing to do with towers! The DUP feature I was referring to is a way to make new IDs without having to start from scratch every time. Using an ID that you already have, you choose DUP and then you only have to edit the ID number (and the text tag, if it needs to be changed). It is a very fast way to program a bunch of similar IDs manually. It is explained on page 37 here: http://rsk.imageg.net/graphics/uc/rsk/Support/ProductManuals/2000106_PM_EN.pdf
As the manual says, it refers to talkgroups on the SAME trunked system (and you can also use it on conventional frequencies that are similar).
Since the scanner will hold 1,800 objects at a time, if each ID is counted as an object, I would assume a maximum of 1,7xx (I guess each frequency would also count as an object, so it would be 1,800 less the # of actual frequencies programmed)
Of course if you have multiple scanlists, you would only be able to hold a total of 1,800 so it depends on how many you put in each scanlist (e.g. 10 scanlists with 170 or so ID's each?)
I hope that is correct - someone else jump in here if I am wrong