  We calculate and identify the counterparts of zero-norm states in the old
covariant first quantised (OCFQ) spectrum of open bosonic string in two other
quantization schemes of string theory, namely the light-cone DDF zero-norm
states and the off-shell BRST zero-norm states (with ghost) in the Witten
string field theory (WSFT). In particular, special attention is paid to the
inter-particle zero-norm states in all quantization schemes. For the case of
the off-shell BRST zero-norm states, we impose the no ghost conditions and
recover exactly two types of on-shell zero-norm states in the OCFQ string
spectrum for the first few low-lying mass levels. We then show that off-shell
gauge transformations of WSFT are identical to the on-shell stringy gauge
symmetries generated by two types of zero-norm states in the generalized
massive sigma-model approach of string theory. The high energy limit of these
stringy gauge symmetries was recently used to calculate the proportionality
constants, conjectured by Gross, among high energy scattering amplitudes of
different string states. Based on these zero-norm state calculations, we have
thus related gauge symmetry of WSFT to the high-energy stringy symmetry of
Gross.
