  Making use of virtual observatory data, we present the first comprehensive
sample of optical observations conducted before the explosion times of all
gamma-ray bursts (GRBs) with known redshifts. In total, the fields of 11 such
GRBs were observed by the Near-Earth Asteroid Tracking (NEAT) program from
years to hours before the bursts. Though the typical limiting magnitudes from
these observations are R~20 mag, we find no evidence for a significant
detection of a precursor. The deepest non-detection of precursor emission is
from GRB 030329, reaching down to an absolute B-band magnitude of M_B -18 mag
from 6--1500 days (restframe) before the burst. This is of comparable
brightness to supernovae, which, in some scenarios for GRB progenitors, are
predicted to pre-date a GRB on similar timescales. Since sources cannot be
localized to better than ~500 milliarcsecond (3 sigma) with current large-area
surveys, unrelated supernovae or AGN activity in GRB hosts could be mistaken
for genuine precursor emission. This possibility motivates the need for not
only deep wide-field imaging, but imaging at high spatial resolution.
