The following work flow helps.
Get into conversation mode if not already there. (General settings)
For each label:
- Select the label
- Check the box above the list to select all in the list.
- Check the link that appears at the top of the list to extend the selection to the rest of the labeled conversations.
At this point you have selected all conversations that have at least one message tagged with this label.
This takes half a minute to a minute per label depending on how many messages you are working with.
Are you done?
Check Go to search slot. search for has:nouserlabels This should NOT show any matching labels. If it does then there is at least one unlabeled message in that conversation.
Downside: Sent messages added to this thread will not inherit the labels.
Second workaround:
Work on your filters. By default filters are ANDed together. However you can do things like
from:foo@bar.com OR to:foo@bar.com
in the has text box. This will label outgoing messages as well as incoming ones.
Categories are tabs you can have display in your Inbox to help you organize your incoming messages automatically. You can almost also treat them like labels.
Labels are "tags" you put on messages. You have to explicitly put the label(s) on a message (or conversation), either through direct action or via a filter.
Categories, on the other hand, are Google's automated attempt to "categorize" your incoming email messages. While you can help adjust the algorithm by marking messages on which Google has guessed wrong, it's still Google automatically adding a category to a message for you. Fortunately, you get to choose which of the four extra categories will be used with your inbox and, if you want, you can have none of them.
As far as filters, by and large that counts as explicit action by you and is how you can automatically apply labels to messages that fit some criteria. But it's still entirely your criteria; Google's algorithm doesn't get involved.
Categories can be treated like labels in that you can have them appear like labels on message records when you're looking at a list of messages and while searching (e.g., label:work vs. category:social).
More information from Google Support: Inbox tabs and category labels
Best Answer
The big difference that I see is that when you "Label" a message, it doesn't remove it from the Inbox. But when you "Move" something, it adds the desired "label" and also removes the "Inbox" label.
The Archive button also removes the Inbox label. So, using the "Move" process is the same as first adding a Label, and then clicking "Archive".
As far as selecting many items, you can do it as long as you can create an appropriate search string. For example, say you search for "mom", and you get a list of emails. You can click the "select all" button to mark ll of the messages on that page:
Now, here's the trick: If there were multiple screens of emails that came up because of your search, you will see the following message near the top of the screen (above the email list):
There you have it :)