... at least not in the public documents.

However, if you are talking about the newer P89xV51Rx2 and kin (next time please post the full part number, as e.g. P89C51 (with no other significant characters in the name) is a real part which is "dumb" i.e. no ISP) the bootloader is located in part of the FLASH, i.e. what it returns is not that authoritative either (can be overwritten). For example, recently it has been discovered that there are two bootloaders indistinguishable by the signature/version it returns, yet one of them is crippled of several quite interesting features.

JW