It doesn't matter if I do one mirror or a bunch of them. I get the same number of files.
aptly mirror create -architectures=amd64 -filter='Priority (required) | Priority (important) | Priority (standard)' -keyring=/root/.gnupg/trustedkeys.gpg focal-main http://us.archive.ubuntu.com/ubuntu/ focal main
aptly mirror create -architectures=amd64 -filter='Priority (required) | Priority (important) | Priority (standard)' -keyring=/root/.gnupg/trustedkeys.gpg focal-updates-main
http://us.archive.ubuntu.com/ubuntu/ focal-updates main
aptly mirror create -architectures=amd64 -filter='Priority (required) | Priority (important) | Priority (standard)' -keyring=/root/.gnupg/trustedkeys.gpg focal-universe
http://us.archive.ubuntu.com/ubuntu/ focal universe
aptly mirror create -architectures=amd64 -filter='Priority (required) | Priority (important) | Priority (standard)' -keyring=/root/.gnupg/trustedkeys.gpg focal-updates-universe
http://us.archive.ubuntu.com/ubuntu/ focal-updates universe
aptly mirror create -architectures=amd64 -filter='Priority (required) | Priority (important) | Priority (standard)' -keyring=/root/.gnupg/trustedkeys.gpg focal-multiverse
http://us.archive.ubuntu.com/ubuntu/ focal multiverse
aptly mirror create -architectures=amd64 -filter='Priority (required) | Priority (important) | Priority (standard)' -keyring=/root/.gnupg/trustedkeys.gpg focal-updates-multiverse
http://us.archive.ubuntu.com/ubuntu/ focal-updates multiverse
aptly mirror create -architectures=amd64 -filter='Priority (required) | Priority (important) | Priority (standard)' -keyring=/root/.gnupg/trustedkeys.gpg focal-security-main
http://security.ubuntu.com/ubuntu focal-security main
aptly mirror create -architectures=amd64 -filter='Priority (required) | Priority (important) | Priority (standard)' -keyring=/root/.gnupg/trustedkeys.gpg focal-security-universe
http://security.ubuntu.com/ubuntu focal-security universe
aptly mirror create -architectures=amd64 -filter='Priority (required) | Priority (important) | Priority (standard)' -keyring=/root/.gnupg/trustedkeys.gpg focal-security-multiverse
http://security.ubuntu.com/ubuntu focal-security multiverse