What is this NOR feedback loop in the AGC Cross Point Generator II?
This is definitely not an oscillator. The output signal of the circuit is in fact CGMC, which is used to clear the register G after it has been used by multiplication or division operations as an auxiliary register. 

STBE and STBF are the strobe signals for Erasable and Fixed memory.

The whole circuit looks to me like a timing delay generator that is triggered by the memory strobe signals and generates a clear pulse for the G register with a defined length and delay set by the NOR gates' propagation delays.

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