Do Pre-made townie sims wear other outfits?

@DudeNamedWill I expect that they will not turn up in your other outfits unless there is some reason a change of clothes is triggered on the lot or by their action (ie - if they are at a restaurant that requires formal attire, a gym, a pool, on a jog, etc.).

Also, if memory serves they don't automatically cycle to another outfit unless you have a laundry hamper and the outfit they had on before the shower is now dirty so they have a different one after the shower. I don't think the other Sims you're not playing will be showering autonomously, either. I could be wrong since I play with aging off plus other of my settings may have effected what I saw in the past. 

However, I do see my Sims occasionally turn up, when I enter the lot or see them in public, in promo or other clothing item(s) I never chose for them, but this seems to go away when they shower or do certain activities while I'm playing them, and this clothing item(s) is not part of their set outfits.

Bottom line, I think your non-played Sims will normally be running around in their 'default'/#1 outfit.