Boomsplashes are often masked by a problem with the size of the inventory window. It needs to be enlarged in the right-left direction.
It's better to start by assembling the Atysmin, in my opinion.
If the grinch appears to steal the atysmin you need to have enough Hatysmas fragments and therefore not to have assembled the Hatysmas before.
By assembling the atysmin you can gain Atysmas items like star sticks etc. but if the grinch steals it, you get nothing.
I think the chances of hitting the Grinch with a single Hatismas are so low that you should not attempt it.
1. I normally keep it 10 icons wide ... makes it easy to count. Exactly what will I see in my invemtory after I assemble 24/24 ? That is when I have 72/24 Boomsplash fragments ... and I assemple one ... what should I see ? ...widening it I get nothing extra in inventory window.
2. Exactly what am I fighting the grinch and snowman with ? Boomsplashes or boomsplash fragments ?