Using the Clymer and the OEM manual, my disk passed inspection at about .157. Again, my last disk was at .103 without failure, having been used heavily to help stop a sidecar with a 75 lb. dog. So AFIAC, the .14 minimum spec can be adhered to and the .18 value ignored without repercussions of a technical nature. It isn't an ABS related stamp because that same stamp is on the disk that shipped with my 94 non-ABS K75.
As to the riddle of the.18 stamp, since it's in American standard units I think it's reasonable to say that it was introduced early on in the production process to address some US-specific concerns, and then nobody bothered to remove it and in the meantime it's actual purpose has been forgotten. Maybe it's not a minimum use spec at all, maybe it's a spec for the minimum out-of-the-box thickness to distinguish it from an earlier version that was NOT .18 out of the box, like maybe perhaps the one that had the cracking problem or maybe even a short-term interim solution that was used here in the US before the Vaterland got its shit together enough to design and produce the next generation.
Anyone having to have their bike inspected should take these docs to the inspector before paying for the inspection to avoid unpleasant surprises. Inquire specifically which value the inspector considers applicable. Even if your disk is below .157, the inspector might say the .14 minimum throw-away value applies. That's what my inspector said -- as long as it's .14, it's a pass. But YMMV depending on your inspector -- I guess one could just as easily argue that the service range of .157-.173 applies and below .157 isn't acceptable for inspection purposes.
