After speaking with 2 (not well-known) HERP friends of mine yesterday.. we have come up with a speculation about Redfoot tortoises.
Allow me to mention first:
These friends have hatched well over 150 G. elegans.. Indian Star tortoises.
Have successfully established the "Incubation Procedure" for 'Flat-tail' tortoises..

..which requires a "cool-down" period of 5-6 weeks and then returned to needed temps for another 8 MONTHS or so.. (the
FIRST in the U.S. to accomplish) and is currently incubating Platynota (Burmese Star) eggs.
I suspect that we might be able to rely on "our" speculation!
We have come to the conclusion that maybe.. just maybe.. redfoot tortoises don't need D3 derived from UVB - the sun! Or at least not that much of it. Keep in mind the intensity of the sun on the Northern 2/3 of the South American continent.. where "most" redfoot tortoises are native to.
Terry