If you’re seeking just a couple basic hits not on the current map, Marc’s advice should be easy enough to find what midi note they are within BBC and map accordingly. You may have to create custom playing and playback techniques to link them together.
However since you are asking about “full potential”… This has been an ongoing project of mine, with all my percussion libraries including BBC. The unique issue specific to percussion libaries is that many of them spread different recording variations of the same instrument and same articulation across the keyboard. So if you want a medium suspended cymbal crash, they might place this on 3 or 4 keys, each one offering subtle variations, only relevant to playback.
You can read more about the approach I began to take here: I created my first percussion map. Now how can I manually swap midi notes / keys?
In short, you first have to map all the keys using percussion map. This is the easy part, although tedious and time-consuming. The next part is a bit harder and somewhat convoluted – you effectively have to create new playback and playing techniques which are hidden, I call them stuff like hit1, hit2, hit3. Then you have to map these from the percussion techniques window. I select a different notehead for each sound so it’s obvious when I cycle through them (using the keyboard). You would then have to do this for every single instrument and every single sample, and it doesn’t easily translate to other patches even from the same developer since they will often place these keys randomly (since it’s unpitched it doesn’t really matter). So in other words you might get a medium suspended cymbal working great, and then when you go to work on a large suspended cymbal, the patch might have hits on totally different keys - so you have to create different mapping for that one too.
If it sounds like a confusing headache, it is. I honestly shelved this project for awhile because it’s pretty frustrating and something I’ll have to chip away at over time.
More recently I am considering to approach a different workflow where I convert all my unpitched percussion staves to working “pitched” staves, which should make it much easier to move a note up and down and find the sample you want, without having to do all that extra work. However I am not sure if it will be at all possible to “convert” this to a normal unpitched staff after the fact. Obviously I don’t want all my percussion on pitched staves, it would just be for finding the right sample.