Unsigned Overflow
A carry out of the Most Significant Digit (MSD) or Most Significant Bit (MSB) is an OVERFLOW indicator for addition of UNSIGNED numbers.
The correct result has overflowed the number range for that precision, and thus the result is incorrect.
If we could STORE the carry out of the MSD, then the answer would be correct. But we are assuming it is discarded because of fixed precision, so the bits we have left are the incorrect answer.