Getting back to what I was asking you:
What do you mean by 'Your child's birthday cards are always perfect'? What do you mean by 'perfect' on this sentence? How are you measuring this? What do you mean by 'perfection' in 'perfection is better than improvement' ?
The perfect card would be legible, neat, a little funny, a little sweet. No spelling errors. There would be something personal, maybe an anecdote from the previous year. My postive qualities would be acknowledged. Maybe it would rhyme... etc.
I'm a little surprised you need me to explain what it means for a birthday card to improve year to year. I'm guessing you don't have kids; but, can't you remember what it was like making birthday cards as a child?
Anyways, I suppose you could take the qualities I listed above and improve on them year to year. Imagine a birthday card written by a 3 year old in their pre-school class compared to a birthday card from a 20 year old. If the birthday card didn't improve year to year it would be as if the 20 year old had written it each year. The card wouldn't reflect all the imperfections that happen when a toddler attempts to make a birthday card.
So, what I'm saying is, something would be lost, imo, if the birthday card did not improve year to year and instead looked as if a 20 year old had written it each year. It's fun to see how the writing changes and the complexity changes, how the humor matures, etc... One wouldn't see that if each card was perfect all along, from the very beginning.