I have made pics of some of the Cherry boards i have 
1) G80-3000 MX Black, no Diode but a "U"
2) G80-8200 MX Brown, Diode
3) G80-1800 MX Black, no Diode but a "U"
4) G80-11900 MX Black, no Diode but a "U"
For all the boards, no diode on the PCB… And we can see that the “U” are also used on the CPU, they are connected.