Well this is not an answer but the search for one. My daughter has 2 work addresses and one is wrong and doesn't even exist in my Contact list under her name or any other.
Yet if I input the first 3 letters of her name 2 name (hers) will populate and only 2. I did not realise this until recently I accidentally picked the 2nd and it returned a delivery ...
When you are in the channel in which you want to search, just use Command+F on MacOS or Ctrl+F on other operating systems. It will pre-populate the search field with in:#<channel-name> for you.
Otherwise, you need to type it manually, which also works but less convenient.