Label value Coverage issues

[bobosmile1170556238]

First

cat <<EOF | curl -X POST --data-binary @- http://127.0.0.1:9091/metrics/job/memory
memory{code="24", instance="A"} 1
EOF

Second

cat <<EOF | curl -X PUT --data-binary @- http://127.0.0.1:9091/metrics/job/memory
memory{code="25", instance="B"} 5
EOF

Why does the second of these two examples overwrite the first? How can they coexist?