What's a good way to estimate the total number of 6502 or 8051 chips (or workalikes, pin-compatible or not, but not including software or FPGA emulators) ever manufactured or sold?
Added:
(To clarify, for the 8051, I'm asking about a estimate regarding the number integrated circuit devices that execute the original basic 8051 ISA directly using hardwired transistors dedicated at fabrication time for executing the 8051 ISA, or an inclusive proper superset. Similar question for the 6502 ISA. Disregard differences in the originally documented as unimplemented instruction space.)