Desecrate - Missing monster

Hello,

I thought I understood how Desecrate works but I think I am misunderstanding something. Following situation:

I killed Ghastly Spriggan in a map and raised it with Raise Spectre. Then I used a level 1 Desecrate to try to get more Ghastly Spriggan corpses. But no luck. In my Hideout I only got Flame Sentinels (I had 1 active at that time) and some skeletons, I think Bone Stalker or something like that.

I was curious and went to Act 2 because I thought this were the same Spriggans, but there they are Skeletal Spriggons. I raised one of them (instead of my Flame Sentinel) and tried Desecrate. This time, no more Flame Sentinels, but instead Skeletal Spriggans and the same Skeleton monster as before.

1) Why is Ghastly Spriggan never showing?
2) Why is Flame Sentinel only showing when one is already active?

I thought spectre banks worked by Desecrate keeping an "inventory" of my last 10 or so raised monsters and showed these?

Is it my level 1 Desecrate? Was I just mistaken? Or has it something to do with the Detonate Dead changes?

Thanks

Edit: Does the specific gem store the monster, like AG? I just remembered that I changed the Desecrate gem from a level 3 to the level 1 during leveling. I believe that I raised a Flame Sentinel with the new one . I do know that 2 Flame Sentinels were active when I changed the gem (I am not sure, when the monster should be saved, only when raised or also when active). That could at least explain Flame Sentinels.

But Ghastly Spriggan. Can they maybe just not be desecrated?

GGG plz consider making them (ghastly spriggans) desecrateable. I dont think they are op or anything, but i really like them.