  We investigate the effects of extended multi-year light curves (9-year
photometry and 5-year spectroscopy) on the detection of time lags between the
continuum variability and broad-line response of quasars at z>~1.5, and compare
with the results using 4-year photometry+spectroscopy presented in a companion
paper. We demonstrate the benefits of the extended light curves in three cases:
(1) lags that are too long to be detected by the shorter-duration data but can
be detected with the extended data; (2) lags that are recovered by the extended
light curves but missed in the shorter-duration data due to insufficient light
curve quality; and (3) lags for different broad line species in the same
object. These examples demonstrate the importance of long-term monitoring for
reverberation mapping to detect lags for luminous quasars at high-redshift, and
the expected performance of the final dataset from the Sloan Digital Sky Survey
Reverberation Mapping project that will have 11-year photometric and 7-year
spectroscopic baselines.
