Understanding Resource SKU restriction reason codes

Hello,

I am using the SKU REST API (https://docs.microsoft.com/en-us/rest/api/compute/resource-skus/list?tabs=HTTP) to query available VM sizes for each region and I do not understand ResourceSkuRestrictionsReasonCode. There are two codes: NotAvailableForSubscription and QuotaId.

Now, for NotAvailableForSubscription I see many deprecated sizes listed which makes perfect sense, but I also do see some sizes to disappear/reapper from time to time when I do multiple requests and I wonder if this reason code is also used when capacity for such VM size is reached.

The problem is, I want to get full list of all possible (not deprecated) VM sizes, I am not interested in what the actual capacity is and I believe this REST API is the right one to use. Can someone explain me this flag?

The second code, QuotaId, is also a bit weird. From the name, it looks like it should restrict VM sizes my account don't have quotas for, however, on my account I only have basic quotas, yet I see all of the VM sizes. I have literally zero quota restrictions.

The documentation is not really good for this REST API, I hope to find more information somewhere. Thanks!