Here is an example of how a tag can be pulled out of the cards. I mentioned before that vertical left side open cards are easiest & nicer looking. Because it gives the cards a sort of order of pulling out tags top/side/top/side.
And here is a tag being pulled from an envelope. If you'll notice, the envelope is going the "wrong" way. What is normally the top, open flap has been glued down, and it's the bottom that is open. I did this on purpose. (No, really!) I used a template to make envelopes with some paper that matched the papers on my cards. When I folded up the envelope the right way, there was a LOT of opening for the tag to fall out of accidentally. With less of an opening (by leaving the bottom open and the top closed), the tag sat in the envelope a little better.