Memorization is a consistent challenge in ensembles, and I think that a big part of it is an overarching strategy that musicians learn with experience.
When I’m memorizing a piece of music, I am often focusing more on the differences, not details. That is, I recognize that music almost always has elements that repeat, either identically or nearly so. By focusing on the differences and repetitions, I can vastly increase my memorization time.
Consider a jazz standard like “The Way You Look Tonight.” I think a lot of young musicians approaching it might look at it as a 64-measure composition to memorize. Setting lyrics aside (they’re a different beast), though, and we can recognize that 48 of those measures are nearly identical. Then it’s just a matter of noticing that the second “A” section has a pickup melody, and the final “A” typically has a slight extension and repeated phrase.
Any piece can be considered top-down like this, looking at large-scale structure rather than considering each note individually. It’s like giving directions to a destination several hundred miles away. It won’t be effective to include every mile in the directions (“Stay on US-131 for the next mile.” “Now stay on US-131 for the next mile.” “Then stay on US-131 for the next mile.”) You need the important signposts and trust that the driver can manage the in-betweens. The same is true for navigating the music – memorize the road map and differences and trust that your memory can manage the in-betweens.