@Playalot Thank you so much for explaining how I could test my own question about the visiting NPC who I'd been trying to starve (to boost my legacy challenge score).
Using a copy of my challenge file, I deleted a household member so that I'd be left with seven sims.
(1) Add to family without planning outfits first
At a point over 60 hours since locking up the NPC, I cheated to add him to family. He was an elder with a bubbling age bar, which explains why he later died of old age.
But why didn't he starve to death before that?
Well, the NPC's Bladder and Social were close to zero but his Hunger and Fun were about 40%. How could his Hunger be 40% after not eating for 60+ hours?
(2) Plan outfits before adding to family
This time, I used a dresser to "plan outfits," after which I cheated to add the NPC to the family.
In this case, his Social was very low but all his other needs were at 100%.
TL;DR : If you're trying to starve a sim on your lot, don't plan outfits. Entering CAS will refill that sim's Hunger bar.
You ask if this is a glitch, Playalot. I don't know and I keep forgetting to check my household sims's needs after using the dresser.