Just want to clear doubt if you woud have any.
If Customer is using SEP 11 RU7 MP4 & want to upgrade to SEP 12.1 then he needs to upgrade to SEP 12.1 RU4 only.
Check this info in the release notes:
"Supported upgrade paths from Symantec Endpoint Protection 11.0.7.4 to Symantec Endpoint Protection 12.1.x
Supported upgrade paths from Symantec Endpoint Protection 11.0.7.4 to Symantec Endpoint Protection 12.1.x When you plan your upgrade from Symantec Endpoint Protection 11.0.7.4 to Symantec Endpoint Protection 12.1.x, the minimum version to which you can upgrade is Symantec Endpoint Protection 12.1.4. This requirement is due to the updated Java Runtime Environment and PHP components in Symantec Endpoint Protection Manager. Earlier versions of Symantec Endpoint Protection 12.1.x are incompatible with these updated components"