[Aiwendil]

And with respect to the Crossing of the Ice: according to The Annals of Aman Fingolfin and the Noldor began this passage in VY 1497, and according to both The Grey Annals (GA) and The Tale of Years (both published in The War of the Jools), Fingolfin and the Noldor crossed the Straits of Ice in VY year 1500.

And in GA 1497 it is noted that Feanor landed at Drengist: 'In this same year of the Valar (but some seven years after in the later reckoning of time) Feanor came over Sea...' I assume this means that around seven Sun Years into 1497, Feanor lands in Middle-earth -- considering that the passing of the ice must have started after Feanor departed, but still within 1497. But I don't recall any notation that a new reckoning in Sun Years is begun before a full Valian Year had transpired.

I'm not sure I entirely follow what your concern is here. The reference to 'seven years' 'in the later reckoning of time' is, it seems to me, just a convenient way of indicating how much time elapsed between the First Battle of Beleriand and the landing of Feanor in Drengist. So Feanor's landing came near the end of 1497, its exact date depending on when exactly the First Battle occurred. Fingolfin saw the fire at Losgar and then departed over the Ice, presumably not very much later, but did not reach Beleriand for two or more Valian years. The brief mention in AAm at the end of the 1497 annal is, it seems to me, a look forward, made since otherwise AAm would end without telling the fate of Fingolfin's host - it does not imply that Fingolfin reached Beleriand in 1497.

Possible stupid question alert! in suggesting a range for Maedros' travail upon the precipice, should one count a full 9.582 years between the start of VY year 1500 and Sun Year 1? Or should this not be assumed?

Now that's an interesting question. Both AAm and GA seem to say that the Sun and Moon first rose in VY 1500, but no indication is given as to when during that year this occurred. It does seem clear that the new reckoning in Years of the Sun began on the first day that the new lamps were aloft. If that happened at the very end of VY 1500 (i.e. just when the year 1501 would otherwise have started), then of course there would be a full 9.582 years between the start of VY 1500 and the start of YS 1. It might seem a remarkable coincidence if this were the case, but one might suppose that the Valar planned it that way. Alternatively, if the Sun and Moon were raised before the end of the 1500, then I suppose 1500 would be a short year - that is, less that a full 9.582 years of the Sun.