  We explore how the estimated star formation rate (SFR) of a sample of
isolated, massive dusty star-forming galaxies at early cosmic epochs ($1.5 < z
< 3.5$) changes when their ultraviolet (UV) to near-infrared (NIR) spectral
energy distribution is extended to longer wavelengths by adding
far-infrared/sub-millimeter data to trace the reprocessed radiation from dust
heated by young massive stars. We use large-area surveys with multi-wavelength
datasets that include DECam UV-to-optical, VICS82 NIR, Spitzer-IRAC NIR, and
Herschel-SPIRE far-infrared/sub-millimeter data. We find that the inclusion of
far-infrared/sub-millimeter data leads to SFRs that span $\sim$100-3500
$M_{\odot} yr^{-1}$ and are higher than the extinction-corrected UV-based SFR
by an average factor of $\sim$3.5, and by a factor of over 10 in many
individual galaxies. Our study demonstrates the importance of
far-IR/sub-millimeter data for deriving accurate SFRs in massive dusty galaxies
at early epochs, and underscores the need for next-generation
far-IR/sub-millimeter facilities with high sensitivity, field of view, and
angular resolution.
