Can we put this to rest? The soundcard wars ended decades ago.
You started this thread asking to put this "myth" to rest, but other than showing that a 16-bit CODEC was present on the card, provide no supporting evidence that this product line actually delivers 16-bit-quality sound. That would be the way to put the claim to rest. If one cares to waste the time to measure the output and show that, for each of the 65536 input values, a unique, stable voltage level is produced in a repeatable manner, then we will have irrefutable proof of the truly 16-bit pedigree of these cards. Anything less is just as debatable as the 12-bit claim itself.
Personally, I was quite disappointed when I switched to a Sound Blaster 16 Basic at the time. The very first time I ran the Creative demo software, I understood that I had compromised on sound quality to gain software support. Even at only 12-bit resolution, the Ad Lib Gold it had replaced produced far less noise and crackle when playing back digital audio. Yes, the card was properly configured, and the amplifier disabled via the on-board jumper intended for that purpose; it just wasn't particularly good. Part of the problem with the SB16 line seems to be the large number of variants and varying quality of parts used through the years.
All of the reviews I read at the time were in agreement: the SB16, like all other consumer sound cards of the time, did not give full, flat 20 Hz to 20 kHz frequency response. To get that, one had to get into RAP-10 or Multisound territory, and those were hardly gaming cards.