I hear some voices around me, telling that Einstine got the result
of the position of whatever cosmic planets, then putted them as a
proof
for a prediction his relativity should make.

But this is cheating, and such a behavior has been rejected in many
other
theories, as not good.

How come that this was permitted in relativity?

What kinda prediction is that, when you make the prediction after you
already
know the results of what that prediction is supposed to make?