If you add “अभी तक”, then “अभी तक नहीं मिला है” and “अभी तक नहीं मिला” are both be the same I think. Had it been something like “कोरियर 9 बजे तक भी नहीं मिला”, “कोरियर 9 बजे तक भी नहीं मिला है”, could have had a different meaning. (Then we might have used ‘had not been’ for the first one, but even for that ‘is’ is not appropriate).
There are many other places where an ‘is’ can be used in such sentences though, so be careful. For example,
“When the courier is received, we will mail it to you.”
is a correct sentence.