I remember when the ET4000H came out and it was not supported by Windows 3.1 at the time, I had to call MS tech support and they sent me a driver disk that arrived 8 hours later.
To clarify... the ET4000H was the same ET4000ax that was supported by Windows 3.0 and 3.1 already, but with the HiDAC (15/16bit truecolour) fitted instead of the 256 colour DAC. My recollection is fuzzy, but ISTR that it worked with the default driver in 16 colour mode, but not 256 or better, resolution selection may have been limited too.
MS claims that the driver that supported HiDAC came out the 3rd week of April 1992, which would have been 1-2 weeks after the time period I'm remembering, so it sounds about right.
Best support I've ever had for a pirated product.