"team members remembered the code they had recently written better"

Exactly.

A retro every too weeks is too late.

People think of improvement ideas every day. The time to raise the idea is when the idea strikes!

Waiting to discuss it is okay, but raise the idea now! Don't wait!

And if the idea is important, then don't wait to discuss it! Why wait for the retro???

The highly agile companies that we studied were more event-based. They discussed things right after things happened - not in a retro weeks later.