Ai(mage) question

I ve been trying to incorporata icons for various moon ages but Im not exactly sure about the range of returned values and their co-relation to the actual moon phase.
I waited close to a whole month and observed that it returned values from 0 to 29. I thought that I needed 30 icons then to represent the above ages.
Now this month it seems to go up to 28 then returns back to 0 ( New moon). I ve been searching APIs and still cant figure out:
Regardless of whether the providers of astro-info round to closer integers… Does age 15 always correspond to full moon? Or does this change according to how many days of age has the moon for a given month?

so my answer doesn’t exactly answer your question but there is api from Moon-API.com | Real-time Moon Data - Explore the Moon’s Phases and Much More which is free for 500 request per month which has unique feature of returning moon phase as emoji another api but again the data format is the difficult to get to since each providers have different formatting once even though its same old json.