The implementation needs to enforce a strict priority of DSS over SACK and ADD_ADDR.
TCP options have evolved over a period of time, and I do not think as such any document/guidelines exist on enforcing priority for one over the other, though it turns out be an interesting topic. Also, more TCP options could come up in future for implementing new features. So, it is likely that implementations would follow different strategy when it come to option priority.
FYI, this has come up as an issue before.
TCP options are individual and accepted in isolation. They are easily confirmed only during SYN exchange; anything after that requires a stateful, reliable transmission mechanism for coordination.
There is no way to retrofit any ordering constraints, or prioritization. If you need that sort of feature, it needs to be built inside a single option as “sub options”.
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