  In this paper we study the universality of the results of SQUEzE, a software
package to classify quasar spectra and estimate their redshifts. The code is
presented in \cite{Perez-Rafols+2019}. We test the results against changes on
signal-to-noise, spectral resolution, wavelength coverage, and quasar
brightness. We find that SQUEzE levels of performance (quantified with purity
and completeness) are stable to spectra that have a noise dispersion 4 times
that of our standard test sample, BOSS. We also find that the performance
remains unchanged if pixels of width 25\AA are considered, and decreases by
$\sim2\%$ for pixels of width 100\AA. We see no effect when analyzing subsets
of different quasar brightness, and we establish that the blue part (up to
7000\AA) of the spectra is sufficient for the classification. Finally, we
compare our suite of tests with samples of spectra expected from WEAVE-QSO and
DESI, and narrow-band imaging from J-PAS. We conclude that SQUEzE will perform
similarly when confronted with the demands of these future surveys as when
applied to current BOSS (and eBOSS) data.
  {\it Keywords: cosmology: observations - quasar: emission lines - quasar:
absorption lines}
