Personally, I do all my adjustments by hand, so it's just a matter of time and effort to specialize the overlaps rather than using one guideline that I don't feel fits all cases. Then again, I've not released a fully edited list because it takes so long. As far as the Y175 refit goes, anything being NEWLY PRODUCED from a shipyard would have the refit installed -- even on day 1. That's because they start building in the refits before the ship is finished in anticipation of the new standard. In D2 terms, you can't upgrade ships like in SFC1, so you have to buy new ships. Again, it's a shame D2 doesn't have the refit option.
The trouble comes in where you see AIs being created for missions. Certainly not all ships in the field would have time to get back to dock for refits the first day of a refit year. Then again, they'd certainly have some dock time at some point during the year (argument for 1 year overlap). However, isn't one of the D2 problems that AI can be very weak? Why not give them the better ships and avoid having them get out-of-date versions? Any player ships in the field would reflect captains who had not gotten back for refits yet, since your D7B doesn't just turn into a D7K overnight (visions of Cinderella).
Again, this is all subjective. These are arguments from one side, and I'm sure there are at least as many from the other sides.
Keep up the good work.
PS: I'm still a little confused on that 2/3 rounding down you mentioned. In the case of a ship with 5 fighters or 5 mech links, 2/3 is 3 and 1/3, or rounded to 3. But, a ship with 10 fighters (hypothetical) would get 6 and 2/3, or round up to 7 rather than down to 6. What you're saying is that latter example would result in a 6? Just trying to understand your approach.