[LAD] successive note on midi events

Hi, I'm pretty sure I've seen this dealt with on the list before, but can't find it. With the program I'm fumbling around trying to create, it will be possible for successive note on events for the same pitch to occur without note off events intervening. Does the MIDI spec allow such things? The bash-script prototype of the program did this, and, I believe, the soft-synths used, acted appropriately - that is, re-triggered the notes. So I guess the question is, does it make any difference if I add-in the note-off events - which, thinking about it, is going to be tricky because, basically, although the program is sequencing, it will be real time and is not psychic! Cheers, James.