  Bottom-up hierarchical formation of dark matter haloes is not as monotonic as
implicitly assumed in the Press-Schechter formalism: matter can be ejected into
tidal tails, shells or low density `atmospheres'. The implications that the
possible truncation of star formation in these tidal `debris' may have for
observational galaxy statistics are examined here using the ArFus N-body plus
semi-analytical galaxy modelling software.
  Upper and lower bounds on stellar losses implied by a given set of N-body
simulation output data can be investigated by choice of the merging/identity
criterion of haloes between successive N-body simulation output times. A median
merging/identity criterion is defined and used to deduce an upper estimate of
possible star formation and stellar population losses. A largest successor
merging/identity criterion is defined to deduce an estimate which minimises
stellar losses.
  In the N-body simulations studied, the debris losses are short range in
length and temporary; maximum loss is around 16%.
  The induced losses for star formation and luminosity functions are strongest
(losses of 10%-30%) for low luminosity galaxies and at intermediate redshifts
(1 < z < 3). This upper bound on likely losses is smaller than present
observational uncertainties. Hence, Press-Schechter based galaxy formation
models are approximately valid despite ignoring loss of debris, provided that
dwarf galaxy statistics are not under study.
