New firmware versions are announced in CP UserCenter and in Embedded GAiA WebGUI. CPUSE on GAiA appliances is a very different engine and ecosystem that does not include SMB devices!
To "believe that CP has no way to distinguish firewalls with valid subscription vs. out of subscription and hence it never prompts you that a new build is available" is both very wrong and building maybe on a great lack of experience - i have seen the message that there is a new firmware available on SMS rather very often during the last years 😉
CCSP - CCSE / CCTE / CTPS / CCME / CCSM Elite / SMB Specialist