I was going through my Survival Guide just to see what I have collected, and to my surprise, there were several Legendary Outfits (And one Advanced Outfit) shown that I never collected.

Among the things I've never collected:

Advanced:

Wrestler Outfit

Legendary:

Heavy Leather Armor

Heavy Vault Suit

Heavy Wasteland Gear

Heavy Battle Armor

Heavy Raider Armor

Heavy Merc Gear

Expert Lab Coat

Expert Jumpsuit

Expert Radiation Suit

Elder Robe

Wasteland Surgeon

Sheriff's Duster

Commander Fatigues

Commander Uniform

Scribe Rothchild's Robe

Same issue is not evident in the Weapons side. Why did all these outfits suddenly appear in my Survival Guide?

And just so that no one assumes, I didn't get any Legendary dwellers with these outfits, nor did my explorers find them. If they had, I would have kept these outfits in my inventory or dressed a dweller in them.

I have the wasteland surgeon outfit, loads of wrestler outfits, Elder robe and Scribe rothchilds robe. Hoping to get the Sheriff duster one day

I landed the wrestler outfit with a rare Dweller card from a Lunchbox. It looks awesome!

Expert Lab Coat comes with Dr. Li, Sheriff's Duster with Lucas Simms, and Rothchild's Robe with Scribe Rothchild (obviously). I'm sure many of those others mentioned come with legendary characters as well.

I understand they come with Legendary characters, but I never got them, but somehow these outfits appeared in my Survival Guide as if I had.

That's what I think is weird.

OOOOOOOOOOhhhh I see what you are saying now. That is weird!

You can also get them alone from a lunchbox (i.e., without the dweller inside it) or pick them up in the wasteland. That is to say, you don't need to get Eulogy Jones to get his outfit or the Blackhawk.

you can find those exploring, one of your dudes probably hit a jackpot or something

i have found bittercups outfit in the wastes