I for one think that the SR-71 has not only been replaced, but its
replacement has been replaced. in other words, there have probably
been two generations of ultra-fast spy planes beyond the SR-71.

The SR-71 was made in the 60s. probably by the late 70s or early
80s, a sucessor to SR-71 was flying.

and by now, the sucessor to the SR-71's sucessor has, at least been
tested, if not put into service.