The SR-71 won't be anywhere near the first tanker when it needs fuel again. The fuel itself isn't common to most aircraft, which means the tanker has to carry fuel specifically for it so it.
The thing that made it obvious to me that there was a replacement for the SR-71 was that when they retired the aircraft, they didn't retire any of the tankers. That meant there was now some other unknown aircraft flying that also used JP-7, and it must therefore be the replacement for the SR-71.
Note that JP-7 is so hard to light on fire that if you throw a match into a bucket filled with JP-7, the match will get snuffed out. You've got to be a lot hotter than a match to light that stuff.
The same is not true of JP-7.