In Lilo and Stitch (2002), Stitch is referred to originally as '626'. We later (by later I mean a few movies later and several years) find out that Stitch is referred to '626' because he was Jumba's 626th experiment. At the time of the first movie we do not know about Jumba's other experiments.
My question is why was Stitch referred to as '626' before we knew there were more experiments? Was it the case that it was always known by the writers that Jumba had created other experiments and Stitch was the 626th but it was just not referred to on the screen?