->From P89C66X datasheet right under the table it say that:

NOTES:
1. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only and
functional operation of the device at these or any conditions other than those described in the AC and DC Electrical Characteristics section
of this specification is not implied.
2. This product includes circuitry specifically designed for the protection of its internal devices from the damaging effects of excessive static
charge. Nonetheless, it is suggested that conventional precautions be taken to avoid applying greater than the rated maximum.
3. Parameters are valid over operating temperature range unless otherwise specified. All voltages are with respect to VSS unless otherwise noted.

-> From MFRC500 datasheet at the end of document, in difinitions table it says that:

Limiting values
Limiting values given are in accordance with the Absolute Maximum Rating System (IEC 134). Stress
above one or more of the limiting values may cause permanent damage to the device. These are stress
ratings only and operation of the device at these or at any other conditions above those given in the
Characteristics section of the specification is not implied. Exposure to limiting values for extended
periods may affect device reliability.




Thanks