  We study the production of $K^+, \rho, \omega$ and $\phi$ mesons in $p +
^{12}C$ reactions on the basis of empirical spectral functions. The high
momentum, high removal energy part of the spectral function is found to be
negligible in all cases close to the absolute threshold. Furthermore, the
two-step process ($pN \rightarrow \pi N N; \pi N \rightarrow N + K^+, \rho,
\omega, \phi$) dominates the cross section at threshold energies in line with
earlier calculations based on the folding model.
