Selecting specific data from an Ansible register

I'd really appreciate some help on correctly selecting data from a register in ansible. The following code almost works... :)

I create an AWS VPC here, I register the information in 'vpc'. I then refer to vpc.

  - name: Create VPC and Subnets
    ec2_vpc:
      state: present
      cidr_block: '{{ ip-range}}'
      resource_tags: { "Name": "{{ vpc_name }}" }
      region: '{{ region }}'
      subnets:
        - cidr: '{{ pub-subneta }}'
          az: '{{ region }}a'
          resource_tags: { "Name": "Public Subnet 1" }

        - cidr: '{{ pub-subnetb }}'
          az: '{{ region }}b'
          resource_tags: { "Name": "Public Subnet 2" }

        - cidr: '{{ priv-subnet1 }}'
          az: '{{ region }}a'
          resource_tags: { "Name": "Private Subnet 1" }

        - cidr: '{{ priv-subnet2 }}'
          az: '{{ region }}b'
          resource_tags: { "Name": "Private Subnet 2" }
      internet_gateway: True
    register: vpc

That works well. It creates the VPC with the 4 subnets. I then want to launch a NAT instance in a specific subnet which I tried to do by specifiying the subnet as follows:

- name: Create NAT instance
  ec2:
    state: present
    key_name: '{{ ssh_key_name }}'
    instance_type: '{{ nat_instance_type }}'
    image: '{{ nat_ami }}'
    region: '{{ region }}'
    wait: yes
    instance_tags:
      Name: "natsrv01"
      Description: "NAT Server"
    assign_public_ip: yes
    source_dest_check: false
    vpc_subnet_id: '{{ vpc.subnets[0].id }}'

This is where it doesn't work as intended. I'd assumed that the register would contain invformation in the order it was defined/created but that's not the case.

Using debug I can see that the 4 subnets are in a random order in the register. e.g. on one attempt "Public Subnet 2" was identified by 'vpc.subnets[0].id' and on another attempt "private Subnet 2" was the first in the list.

Can someone suggest how I can reliably & repeatedly select "Public Subnet 1" from the register please?

An example of the data in the register:

 "subnets": [
        {
            "az": "eu-west-1b",
            "cidr": REDACTED,
            "id": "subnet-REDACTED",
            "resource_tags": {
                "Name": "Private Subnet 2"
            }
        },
        {
            "az": "eu-west-1a",
            "cidr": "REDACTED",
            "id": "subnet-REDACTED",
            "resource_tags": {
                "Name": "Public Subnet 1"
            }
        },
        {
            "az": "eu-west-1b",
            "cidr": "REDACTED",
            "id": "subnet-REDACTED",
            "resource_tags": {
                "Name": "Public Subnet 2"
            }
        },
        {
            "az": "eu-west-1a",
            "cidr": "REDACTED",
            "id": "subnet-REDACTED",
            "resource_tags": {
                "Name": "Private Subnet 1"
            }
        },