Yowie rarity question

I just added three more Yowies to my US collection (yay!), but it's gotten down to figures that are hard to even find photos of (except on TAW). I'm curious, I know some series have a chase piece that is much harder to find (especially the glass frog), but are all the other figures in a series distributed in the same amount, or are some of them released in greater numbers than others? Did every series have a chase piece, and if so, which ones are they? I see a lot of guanaco from series 4 for sale in lots, often in duplicate, but the only elephant seal I've ever seen from the same series is $30. Just wondering if we know why, or if these hard to find ones are just more popular and not sold as much, or if it's purely just random that there seem to be thousands of phantasmal poison frogs but no palilas.

I could be wrong, someone please correct me if so.

I think the first series or so released all the models in roughly equal amounts. Then they started making certain models in lesser quantities. To some extant I think this reflected the classification of the species in real life (the more endangered it was the fewer figures there were). But I am unsure on the real numbers. The glass frog in particular, as well as a skateboarding celebrity bull dog, and the new giraffe calf of the babies series are "chase pieces".

I will note that certain regions of the country seem to get different frequencies of models too. For me something I found rarely in the Pacific Northwest region of the US was common to say, Kelly in the Southeast region, and vice versa.

It seems to me that at first, figures were more evenly distributed as Paige said.
The bald eagle was supposed to be a chase figure, but I had several pass through my hands. I would love a glass frog, but have yet to find one. But then, I've given up trying.
There may be a difference in region- I also had a few of the star tortoises, but many had a hard time with that. And I would'nt have a bee if it weren't for trading. Different areas get the new waves at different times, it may be related to that.
I think it may be a combination of factors- rarity of the figure, its desirability, its distribution... I had lots of palilas at one point. But they're a pretty enough figure to perhaps appeal outside the toy collector sphere. Some of the smaller and perhaps less attractive figures may have tended to end up in the trash.
It seemed nobody could find the bulldog when it was released. Now I see it on eBay somewhat often.

Thank you both, that makes sense with them being distributed differently around the country. I have never bought any new, so I didn't have to sort through finding lots of original doubles. It does make sense that the earlier sets were more evenly made because those were the easiest ones for me to complete--except that darn palila, haha.

Weird if they did choose to distribute them based on how endangered the species is, since that can be hard to do in a comparative way. Interesting, though.

I haven't seen the skateboarding dog, haha. I will have to keep an eye out. That's a strange thing to throw in the mix.