In a gen 8 random battle earlier today, I went to calc how much damage my Coalossal would do... and I think Coalossal is just missing from the list of inputs?
You can see what I'm talking about here: https://imgur.com/a/x93FvME
Coalossal-Gmax shows up, and you can see in the second picture that both base- and Gmax-forms for other mons (e.g. Copperajah) are listed, so I think it's a Coalossal-specific issue, not a widespread one. It's also entirely possible I was just doing something wrong (still relatively new to competitive and don't have a ton of experience with the calculator) but I was very confused
coalossal only has its Gmax set, it only has 1 set. There is no regular coalossal set