The really rare 13* ?

So I'm wondering if you could tell me if you only seen them drop from rare variations of the bosses of can they drop from the regular bosses im not asking about rev weapon

I have assumed from the rare variants, but unable to confirm because the drop rate for them is ridiculously low.

Probably over 500 normal variant and around 100 rare for Gunne so far and haven't gotten one yet.

I found a stelk from the rare version of bar lodos. I do not think they are exclusive to rare bosses but they drop more items so it will increase your chances. Like how Saiki drops from the regular version of the boss but most people seem to get it from the rare version due to the drop tables.

Thanks for the info I got the Aura soaring blades from night fall rare gwhal spider I was wondering if its possible to get from regular boss