How to most efficiently manage excess cards when upgrading in Clash Royale?

If you open a gold or magical chest, it's not uncommon for you to end up with an excess of a particular card, more than you need to upgrade.

Initially, it appeared that if you upgrade, the excess copies are simply lost. Which is a bit annoying, but losing one or two copies of a common card is no big deal.

However, I recently acquired the Minions card for the first time from a Gold chest, and I got quite a number of them. I'm not sure how many but, crucially, I was able to upgrade twice from the one chest drop. So I didn't lose the excess. It's the only time I've upgraded a card where I had enough to upgrade more than one level at once, so I don't know if that was what made the difference.

So

• What rules govern whether or not you lose excess copies of a card when you upgrade?
• If no-one in your clan is "requesting" copies of a card you have an excess of, is there anything you can do to stop them being wasted when you upgrade?

Solution 1:

The "lost cards on upgrade" is an illusion. (Well, poor interface design, to be percise.)
The upgrade animation shows draining of all cards, but the extra cards are actually saved. If you have enought cards, you can even upgrade a card multiple times in a row.

You should feel free to upgrade your cards without a worry. (Other than spending too much gold.)