Buth for Forth you can have a totally working software floating point
made from the people whose later would set the IEEE standard.
Think about very small microcontrollers without FP in hardware, you can be sure that a software FP implementation will perfectly work under the standard thresolds.
Okay, I guess? I appreciate having a well-verified library when I can't have floating point hardware, but I'm never in that situation and I really don't see how it's relevant to this discussion. Any floating point implementation is going to have rounding problems, including IEEE. The example above is IEEE.