BleManager parses the advertising data to keys and values and returns a map with those pairs.
This is why there is really no reason to get the complete data. You will just need to parse it yourself.
The meaning of the various keys and values depend on the specific peripheral that you are communicating with.
You can see the information with:
Dim bc As ByteConverter
For Each k As Int In AdvertisingData.Keys
Log($"${k}: ${bc.HexFromBytes(AdvertisingData.Get(k))}"$)
Next