I wouldn’t call it common. I’d class it as un commmon.
I would class it as rare, dude.
There is not a lot of rare spawns where I am.
It used to be rare for me in California like I only ever saw one in the wild than in September and October I would see one or more a week in the wild. I had like 10-15 before CD (3 of them hatched)
Just wait for an event, I’m sure Beldum will be boosted in an event sometime.
More strange things like this happend. I had a beldum, caught it, then changed in a belsprout. (Not as bad as a shiny changing in a regular, but strange it is.)
So don’t know of the CD bugs where ment to happen or just sloppy coding.