I have been working on a mod of which the basis is a lot of new default outfits made up from various other clothing mods (that i have creators permission to use). However I have run into a glitch wherein after succesfully introducing about 50 new default outfits and getting them to appear properly in game on the NPC's ..then in a upgrade of the same mod I created about 24 newer default outfits..some of the older ones are no longer evident and the NPC's are nvde. Which brings me to my question : is there an upper limit of new created default outfits?

What do you mean? You cannot create a 'default outfit'. You can create an outfit, then set it as the default outfit on an NPC.

You should be able to create as many outfits as you want. And the default outfit should always show up on the NPC provided nothing else is overriding it. (Scripts to change it, etc)

Ok, to clarify. I created initially 50 new outfits from other than vanilla resources and set them as the default outfit fo a large sector of npc's. The intial 50 all showed up properly on the respective npc's, played through two games with no issues. Recently I wanted to add more outfits and created about 24 from new non vanilla resorces and some of the old outfits that showed up properly were no longer in evidence. No other mod is overwriting the npc's and my mod is last in the load order.