Photos expiration date when only one AP has Memory Maker

[PlutoNotPlanet]

My partner and I always go to the parks together. Only my AP has Memory Maker. One of us will tap the magic band after the photos were taken.
I thought all photos expire after 1 year. But I just realized some of our early October photos disappeared from my album.
Is it a glitch? Or is that because those not tapped by my magic band would expire in 45 days?
Thanks in advance!