Here we place our meters at the bottom of the mast
That is, the PoCo rules not just to the meter, but up to the first overcurrent device. Everything upstream of that point is sealed by the PoCo. Therefore, I infer that PoCo rules apply.
(As a side note, have you ever noticed that most meter pans do NOT have any UL label on them?)
Does the NEC have a section on services? Sure, it does. This section, however, is largely irrelevant when there's a PoCo involved.
In practical terms, there might be an issue in areas of great smowfall. Since we usually use the "all in one" style of combined meter / disconnect / panel, it's not impossible for the PoCo to want the meter placed so high that some of the breakers are higher than the NEC permits.
As for the thread specification ... many factory-made electrical parts have straight threads, rather than tapered. That's not the issue. The NEC specifies tapered threads for "field made" threads ... which I consider applies to any threads you make, or have made.
