Pro service packs should be cumulative (if they're not already so). Most installs and updates are performed by administrators, as most users do not have the rights to self-update the software. Administrators should not have to stack up service packs, and the latest service pack should be cumulative of all previous service packs. If this is already the case, then the release notes should indicate such. Speaking of installation, service pack release notes should include the same silent install instructions as the product (silently deploying a .msp is sort of self explanatory, but you never know!).