Being picky, System 7.5.3 was the one that they released. 7.5.5 requires a small upgrade.

However Apple were very smug during the Y2K fuss. Apple's Y2K support was a single page (rightly) telling us not to worry about their products. They told us that System 6 onwards was Y2K safe, as was GS/OS 6.0.x. Date patches were required for 8 bit date cards for the Apple II, but that is a periodic requirement anyway.

Are any versions of Mac OS non-Y2K compliant?