Hi Kalati,
I hope the following helps to clarify the issue at hand.
Let's assume all eggs you hatch each day are fully incubated, making their chance of hatching successfully 85%. The probability of hatching at least 1 failure per day in the above scenario can be calculated as follows:
0.15 + 0.85 * (0.15 + 0.85 * (0.15)) = 38.5875%
Another way to think of it is by looking at the probability of hatching all eggs successfully. Here is the math for that:
.85 ^ 3 = 61.4125%
And if you subtract that from 100%, you get back to the 38.5875% number.
We do log all failed hatches, but unfortunately, we don't have records of all successful hatch attempts. As such I cannot calculate your exact fail rate. If I go off of the amount of creatu you own that have been born since May, you would be at about a 19% failure rate. Of course, if you bought, sold, traded, or in any other way moved your creatu around, this number becomes less accurate.
I've also verified that no changes have been made to the math that this system is based on.
Please let us know if you have any other questions.