Regarding your last point, the specs might say 2.6 min HTHS but it's actually tricky to make a commercial oil 'tight' against the minimum spec. The quality of individual batches of base oil, DI & VII can bounce around; not by much but they do. If you aim for 2.6 dead, you might occasionally blend up a batch of oil with a 2.54 cP HTHS which is nominally off-grade (remember blend plants work to FIXED formulations. They are generally never tweaked or trimmed to suit). For this reason, most commercial blenders blend conservatively so HTHS is often higher than the spec permits.
If also worth pointing out that sometimes 'the system' works against you. Euro A3/B3/B4 xxW-30 oils not only have to meet 3.5 min HTHS but also 12.5 cst max KV100 & sometimes the two specs can be mutually exclusive. Unlike in the US, 10W30 engine oils are almost unheard of in Europe because of the impossibility of meeting both specs at the same time. To get to 3.5 min HTHS you sort of need the KV100 to be 12.7 cst whereas a commercially acceptable, blendable 12.3 cst KV100 might only yield an HTHS of 3.35 cP.
I suspect, if you went out & checked, there are probably quite a few xxW-30 A3/B3/B4 oils out there that are like this & technically off-grade for HTHS. However as HTHS is not a widely available test, this anomaly is hardly ever picked up on. It might also part-explain why 5W40s are pushed because these circumvent this issue.