It doesn't matter, because they produce the same result.
And those ratios are based on the
calculated outer diameters (or, if you prefer, calculated revolutions per mile) of the tire sizes.
Only if you're using some figure other than the precise calculations based on the nominal tire sizes. Tire manufacturers may have specs on their websites showing slightly different numbers, but these are just as likely to be due to rounding in the calculations, as they are to be actual measurements of the tires. Either way, differences under 0.2 percent are pretty insignificant compared with some other factors; see below.
As for the TCS controllers, it's also quite possible that there are errors in the part number database. I've heard about this and consider such errors the most likely explanation. (I base this conclusion in part on the existence of differences in part numbers between the automatic and manual transmission for the same year NSX, for which there is no logical explanation I can think of.)
The fact is, there are lots of sources of possible differences in tire dimensions. Different make/model tires labeled with the same size are not necessarily exactly the same size. The difference in diameter between a tire that is brand new with full tread depth, and the same tire that has worn down to the treadwear indicator bars (2/32"), is about 2 percent. And the TCS operation itself undoubtedly has some variation in it; e.g. if the ratio of rear-to-front stock outer diameters is 1.0775 (as on the '91-93) and the system requires that the ratio stay within 5 percent of that figure, it's not like the TCS will never activate with tire size ratios of 1.1274 and will always activate with tire size ratios of 1.1276. So while you can carry out calculations with total precision, there is always a "fudge factor" representing these and other variables.
Although the TCS supposedly operates allowing a ratio tolerance of 5 percent, I've found that if you keep the rear-to-front ratio within 3.5 percent of stock, you shouldn't have any problems with the TCS. Go for the full 5 percent, and you might (or might not).
The calculated ratio of the rear-to-front outer diameters (and of revolutions per mile, which is a mile divided by the tire circumference) on a '94-01 NSX is 1.0465. So theoretically you can use tire sizes with a ratio of 0.9965 to 1.0965 (5 percent difference from stock), but as a practical matter, you shouldn't have any problems if you keep it between 1.0115 and 1.0815 (3.5 percent difference).
Here are calculated ratios for the best 16"/17" tire size combinations:
205/45-16 and 245/40-17: 1.0624
205/45-16 and 255/40-17: 1.0760
215/45-16 and 245/40-17: 1.0465 ('94-01 stock)
215/45-16 and 255/40-17: 1.0598
And for the best 17"/18" tire size combinations:
215/40-17 and 255/35-18: 1.0528
215/40-17 and 265/35-18: 1.0644
The bottom line: You shouldn't encounter any TCS problems with any of these combinations of tire sizes on any year NSX. And don't worry about matching the ratio exactly, since differences of a few percent are not a big deal.
(You can look up the ratio of calculated outer diameters of any two tire sizes using a tire calculator like
this one.)
HTH