Curious if there is any protocol for CX to determine priority for these things? Aka, is there a ranking for DMs that check-in agents can see? Any color here?

Personally, I have received all three - birthday (2x), anniversary (5 year), and milestone (500k, 750k, 1mm) regularly in the last 5 years. And admittedly, I am nowhere near as valuable a DM member as I was a few years ago - my spending has dropped significantly. There were 2 or 3 years in my last 5 when the amount spent on on my butt on CX metal air tickets was very significant, but that has plunged in the last 2 years. Still easy to keep DM, but the amount to CX is far less. Although my spend is about to pick back up significantly again in the near future, CX has no way of knowing that, and yet I've still been getting these things quite generously. Most recently, I got upgraded on two separate long-haul sectors for the same milestone.

Originally, I figured I got these types of perks because I was likely spending more than the average DM, and they had some type of ranking system (which was once told to me by a SIN check-in staff, but maybe she was clueless). I also either buy my tickets personally or my (own) company does, aka a corporate policy or travel agency isn't guiding my hand towards a decision. So I thought maybe they could somehow figure out that an individual was 100% responsible for the purchasing decision and basically spending my own money to boot. But no doubt, in the last 2 years, I am spending an average, or maybe even below-average, amount as DM, and I still felt CX has been incredibly generous in handing out freebies to me as a lower-quality DM. So it makes me wonder if they just do their best to accommodate based on loads, etc. and see where the chips fall? Hence I was more lucky than anything else?

At the very least, despite whatever shortcomings I may whinge about on here from time to time, I find myself extremely loyal to CX and highly appreciative of my experience as a DM. I also appreciate that although my spend has dipped as a DM, I still have been treated with the same amount of courtesy as I was when I was flying even more, with almost all full fare J and paid F tix (currently, my F flying is primarily upgrade awards or op-ups, and I have purchased discount J and PEY + upgrade awards to sit in J class).

That is a very long way of saying I have gotten all the anniversary/etc upgrades, both as a higher-value DM and a DM spending less.