So searching the fossil record - even combined with looking for craters, Ir spikes, shocked quartz, etc - isn't a very powerful way to find (or rule out) a Nemesis (or Planet X).
How about a survey of parallaxes? How powerful a technique would that be?
The most recent, and perhaps best known, such survey was HIPPARCOS
; what regions of parameter space* do the results from this mission leave open for a Nemesis (both the HIP and Tycho catalogues)?
*let's assume any such unseen companion is in an orbit around (or with, if you prefer) the Sun, and has been in such an orbit for at least a billion years.