Peter,
"This now "unobtanium glass" was used in one of the three elements of the AP155 oil spaced refractor...that even Christien himself has acknowledged has better I/R correction than their latest 160mm F 7.5 flagship refractor."
the "NASA glass" (KzFS-1) is actually inferior to both Fluorite and FPL53 as far as "abnormality" of dispersion. I'd be surprised if a modern EDT (with two best matching Crowns) couldn't surpass what the old 155 could do.
See copy of Roger Ceragioli's analysis of APO refractor lenses (now only kept at Rohr's site AFAIK)
KzFS1 150mm f/10 Oil-Spaced Triplet maximum chromatic focal shift : 794 microns
FPL53/ZKN7 150mm f/9 (!) Oil-Spaced Triplet Apochromat maximum chromatic focal shift : 59 microns
http://rohr.aiax.de/chapter%204b.htm
Yes, it looks like in far IR FPL53/ZKN7
may get worse, but where it counts (400-800nm) it is far superior.
Bratislav