There are caching policies for fastdl.mongodb.org and downloads.mongodb.com that cause --useLatest to download day-old
or possibly month-old binaries even after the push task has succeeded on the older branches. Changing to use the /tasks/<task_id> endpoint (for example) would make it possible to download the files directly from S3.
An unfortunate consequence of using Evergreen to download binaries from older branches is that we would tie build variants across different mongodb-mongo-* Evergreen projects together when we haven't necessarily been consistent about naming. This means it won't always be possible to download the binaries from the build variant with the same name as the one that exists in mongodb-mongo-master and we may need to keep an explicit mapping in etc/evergreen.yml.
We must also make a decision about whether we should depend on the push task succeeding, or only depend on compile, jsCore, dbtest, and replica_sets_jscore_passthrough succeeding as
SERVER-35972 has changed for the 4.0 and master branches.