The number 6000 is bounced around a lot as being how many original Apple II rev.0 systems were made between June 1977 and mid-1978 before the switch was made to rev.1 motherboards. But I've never read anyone confirm the accuracy of this number. I understand 6000 is specifically referenced in a service manual, but it is unclear whether that context refers to system serial number or that of the motherboard itself, as from the very start there was a gap between the motherboard serial numbers and the A2S1-XXXX system serial number on the outer case.
The highest rev.0 system I have seen is A2S1-5753, and it has a motherboard #6064. I personally own system A2S1-5868 with a rev.1 (that's rev. ONE) board #6179, which the original owner states was the board it came with in July 1978. Therefore the number of rev.0 systems was at most 5867.
However, if you then accept that the number 6000 was all along a reference to the total number of MOTHERBOARDS made, NOT systems, then the number decreases further. I believe MB serial numbers started at 100, so #6064 actually means the 5964th board made. So 6000-5964=36 may indicate that only 36 complete systems after this one "finished out" the inventory of rev.0 boards Apple had on hand. With this logic, the last rev.0 system would have had the serial number A2S1-5789 with MB #6100.
So that is my pet theory that only 5789 complete rev.0 Apple II systems were ever made. For all practical purposes, saying "around" 6000 systems is appropriate, but nailing down the exact number would be interesting for historical accuracy.
Thoughts? Additional insights?