I'm a bit slow on the uptake, but now do understand the concept of Modal. I also proved to myself that with G90 and G91.1 in the same block, G90 causes Distance Mode to be set Absolute but then it is put back to the default value when Mach3 finds G91.1. Since my default values were Distance Mode: Absolute and IJ Mode: Incremental, it all worked for the wrong reason. I'm correctly the article now and will publish the update soon.
Thanks to all that helped me understand this bowl of spaghetti!
Rick