Hello Mark,
Thank you for your post. The hotfixes/security bulletins can be applied as and when Adobe releases them. You only need to install "a" hotfixes/security bulletins once. We keep on releasing new hotfixes/security bulletins as per the vulnerabilities and security threats. So whenever a new hotfixe/security bulletin is released, Adobe recommends their user to apply the same.
Let me know, in case you have any concerns further.
Regards,
Anit Kumar