After reading over the EPA letter[0], I can't help but wonder whether the final paragraph gives a "bad faith out" to John Deere and their ilk. You could disingenuously interpret the "increment of time necessary to effectuate the repair" to mean the time it would take an official John Deere service technician with a full suite of tools to make the repair.

The following sentence admittedly muddies it a bit, but in general the suggestion that John Deere can still be the arbiter for when the machine can / cannot run without the environmental system in the loop seems like a significantly less meaningful change than what is described on the EPA.gov website.

[0] https://dis.epa.gov/otaqpub/display_file.jsp?docid=64859&fla... -- It's only 3 pages, very quick read