The promises of retirement, presented during the beginning of the animal revolution, is something that has become obscure in the animals' memory.
We can arrive at this answer because:
In Chapter 9, the animals are already hopeless about the revolution they caused.
This is because they continue to live oppressively, do not have access to the rights they were promised, and feel they are being exploited by the pigs.
A proof of this is that the promises of retirement, which everyone received, were never fulfilled and are just a dark memory in everyone's mind.
This shows that the animal revolution took away an oppressive system to create another oppressive system, showing that whenever a single group is in power, oppression operates.
