Some releases are stored as revision in the graph (maybe due to an old bug in the git loader?)
For example, look at
https://archive.softwareheritage.org/api/1/origin/2695882/visit/12/
you will see that only 1.0-rc7 is correctly stored as a release, all the others are, incorrectly, revisions.
"refs/tags/0.9.1": {
"target": "45b0039a63c5da3164c6c2c3ff5deabea09ae4ba",
"target_type": "//revision//",
"target_url": "/api/1/revision/45b0039a63c5da3164c6c2c3ff5deabea09ae4ba/"
},
"refs/tags/0.9.8": {
"target": "bfafe56602af035f59dcb6a9bd1ac3d68f193052",
"target_type": "//revision//",
"target_url": "/api/1/revision/bfafe56602af035f59dcb6a9bd1ac3d68f193052/"
},
"refs/tags/0.9.9": {
"target": "d56ae79e43ff1b37534370911c8a78ec7f38d437",
"target_type": "//revision//",
"target_url": "/api/1/revision/d56ae79e43ff1b37534370911c8a78ec7f38d437/"
},
"refs/tags/1.0-rc1": {
"target": "7596fdc31c9aa00aed281ccb026a74cabf2383bb",
"target_type": "//revision//",
"target_url": "/api/1/revision/7596fdc31c9aa00aed281ccb026a74cabf2383bb/"
},
"refs/tags/1.0-rc2": {
"target": "00e81c89c29ff3e58745fdaf7abb68daa1389e85",
"target_type": "//revision//",
"target_url": "/api/1/revision/00e81c89c29ff3e58745fdaf7abb68daa1389e85/"
},
"refs/tags/1.0-rc4": {
"target": "9f1f03ad692f3e98e2c3cb447a54de88e8353b0e",
"target_type": "//revision//",
"target_url": "/api/1/revision/9f1f03ad692f3e98e2c3cb447a54de88e8353b0e/"
},
"refs/tags/1.0-rc5": {
"target": "a7cd1f755cba27f903253c418bdf34bb3962405e",
"target_type": "//revision//",
"target_url": "/api/1/revision/a7cd1f755cba27f903253c418bdf34bb3962405e/"
},
"refs/tags/1.0-rc6": {
"target": "942f90e4ab18c4308a524176f804a88f5ce63454",
"target_type": "//revision//",
"target_url": "/api/1/revision/942f90e4ab18c4308a524176f804a88f5ce63454/"
},
"refs/tags/1.0-rc7": {
"target": "3e7076586691d4e363689fbf5374f833289e0b98",
"target_type": "**release**",
"target_url": "/api/1/release/3e7076586691d4e363689fbf5374f833289e0b98/"
},