Not sure what your question is. I dont see any contradiction with the parent comment. SSE went to version 4.2 (it gets complicated in the numbering and even naming). Only 1 and 2 were included in the base 64-bit ISA.

x86-64 mandates SSE2 as a minimum requirement because it uses the SSE registers in the ABI for implementing float (which requires SSE) and double (which requires SSE2) arithmetic. (The x87 unit, which is what the 32-bit x86 ABI uses, can only do extended-precision arithmetic, which causes a whole heap of problems). Because it's so thoroughly integrated in the ABI, v1 has to have a min-SSE2 requirement.

Subsequently, there were additional instructions added in SSE3, SSSE3, SSE4.1 and SSE4.2, which are all incorporated into the v2 ISA level (along with a few other instructions). Then all of these instructions were given 256-bit variants in AVX, and AVX2 adds some more vector instructions; these are incorporated into the v3 ISA level. And then along comes AVX-512 and naming just becomes a podge at that point...