In the Tag report there are columns with tracked actions and these are counted next to a tag ONLY if the tag was added to the particular ticket before the specific action took place.
E.g.: if you have a rule that adds a tag called "new chat" to a starting chat, then next to the "new chat" tag in the Tag reports you will see the number of "Chats" to which the "new chat" tag was automatically added by the rule when the chat was initiated.
But if you add the "new chat" tag manually to an already running chat, then this particular running chat won't be counted in the "Chats" column since it wasn't added to the chat before the chat actually started. But for example the number of "Finished chats" will increase since the chat was finished after the tag was added to it.
The chart in the Tag report works the same way -- it will show data for a certain 'data type' if that action (e.g. missed chat) happened after a ticket had already been tagged with a tag. So with the specific example of "missed chat" action the tag would have to be added to tickets by an automated rule.