Tempted to say I want contact formalised
I'm assuming this is about going for a court order? I seem to think you've considered this before. Please, please don't. If my kids BPs (who admittedly are very different from you) did something like this I would immediately cease all contact. It would cause immense pain and anxiety to both you and his parents, and it would not be successful.
I know you probably know this, and are just feeling really frustrated; but I think it's worth reiterating how damaging this could be.
Yes the APs have the DC as their priority, but the OP doesn't deserve to be mucked about with or ignored by SS to the extent she seems to have been regularly.
This. I tend to assume that a lot of the frustration and poor communication that miracle has experienced is down to SS. I was shocked when chasing finally revealed that our first letter had not been passed on for 2 months. I was even more shocked when a face to face meeting revealed it hadn't been passed to BGP a year later. Since then I'm like a thorn in our contact co-ordinators side each year.
I know you have had to do the same miracle, but I would not assume that this gets passed to your son's parents in the way you put it to the SW.
All that aside, you get contact letters twice a year- more than many birth parents; more than I would do because, like many parents, I find writing that letter really hard. You really don't know why they have delayed and I think you just have to accept it. I think any parent who writes twice a year values the contact and you want it to continue that way.
YANBU to push for this to work as you do, unfortunately I think it may never be as you want it to be, but at least it's happening.