diff --git a/swh/storage/migrate_extrinsic_metadata.py b/swh/storage/migrate_extrinsic_metadata.py
--- a/swh/storage/migrate_extrinsic_metadata.py
+++ b/swh/storage/migrate_extrinsic_metadata.py
@@ -115,10 +115,39 @@
 
 # not reliable, because PyPI allows arbitrary names
 def pypi_project_from_filename(filename):
+    if filename == "mongomotor-0.13.0.n.tar.gz":
+        return "mongomotor"
+    elif re.match(r"datahaven-rev[0-9]+\.tar\.gz", filename):
+        return "datahaven"
+    elif re.match(r"Dtls-[0-9]\.[0-9]\.[0-9]\.sdist_with_openssl\..*", filename):
+        return "Dtls"
+    elif re.match("pytz-20[0-9][0-9][a-z].tar.gz", filename):
+        return "pytz"
+    elif filename.startswith(("powny-", "obedient.powny-",)):
+        return filename.split("-")[0]
+    elif filename.startswith("devpi-theme-16-"):
+        return "devpi-theme-16"
+    filename = filename.replace(" ", "-")
+
     match = re.match(
-        r"^(?P<project_name>[a-zA-Z0-9_.-]+)"
-        r"-[0-9.]+([a-z]+[0-9]+)?(dev|\.dev[0-9]+)?(-[a-z][a-z0-9]*)?\.(tar\.gz|zip)$",
+        r"^(?P<project_name>[a-z_.-]+)"  # project name
+        r"\.(tar\.gz|tar\.bz2|tgz|zip)$",  # extension
         filename,
+        re.I,
+    )
+    if match:
+        return match.group("project_name")
+
+    match = re.match(
+        r"^(?P<project_name>[a-z0-9_.]+(-[a-z0-9_.]*[a-z][a-z0-9_.]*)*)"  # project name
+        r"-v?[0-9_.]+([a-z]+[0-9]+)?(dev|pre|[a-c])?"  # "main" version
+        r"(\.post[0-9]*)?"  # suffix generated by vcversioner/setuptools-scm/...
+        r"([.-]?(alpha|beta|dev|post|pre|rc)(\.?[0-9]+)?)*"  # development status
+        r"([.-]g?[0-9a-f]+)?"  # git commit
+        r"(-[a-z][a-z0-9]*)?"  # extra suffixes
+        r"\.(tar\.gz|tar\.bz2|tgz|zip)$",  # extension
+        filename,
+        re.I,
     )
     assert match, filename
     return match.group("project_name")
@@ -228,10 +257,17 @@
 
 
 def assert_origin_exists(storage, origin):
-    assert (
-        hashlib.sha1(origin.encode()).digest() in _origins  # very fast
-        or storage.origin_get([origin])[0] is not None  # slow, but up to date
-    ), origin
+    assert check_origin_exists(storage, origin), origin
+
+
+def check_origin_exists(storage, origin):
+    return (
+        (
+            hashlib.sha1(origin.encode()).digest() in _origins  # very fast
+            or storage.origin_get([origin])[0] is not None  # slow, but up to date
+        ),
+        origin,
+    )
 
 
 def load_metadata(
@@ -764,7 +800,23 @@
             # necessarily match the package name on pypi. Therefore, we need
             # to check it.
             if not _check_revision_in_origin(storage, origin, row["id"]):
-                origin = None
+                origin_with_dashes = origin.replace("_", "-")
+                # if the file name contains underscores but we can't find
+                # a matching origin, also try with dashes. It's common for package
+                # names containing underscores to use dashes on pypi.
+                if (
+                    "_" in origin
+                    and check_origin_exists(storage, origin_with_dashes)
+                    and _check_revision_in_origin(
+                        storage, origin_with_dashes, row["id"]
+                    )
+                ):
+                    origin = origin_with_dashes
+                else:
+                    print(
+                        f"revision {row['id'].hex()} false positive of origin {origin}."
+                    )
+                    origin = None
 
             if "project" in metadata:
                 # pypi loader format 2
diff --git a/swh/storage/tests/migrate_extrinsic_metadata/test_pypi.py b/swh/storage/tests/migrate_extrinsic_metadata/test_pypi.py
--- a/swh/storage/tests/migrate_extrinsic_metadata/test_pypi.py
+++ b/swh/storage/tests/migrate_extrinsic_metadata/test_pypi.py
@@ -58,6 +58,33 @@
         ("fake-factory-0.5.6-proper.tar.gz", "fake-factory"),
         ("ariane_procos-0.1.2-b05.tar.gz", "ariane_procos"),
         ("Yelpy-0.2.2dev.tar.gz", "Yelpy"),
+        ("geventhttpclient_c-1.0a-t1.tar.gz", "geventhttpclient_c"),
+        ("codeforlife-portal-1.0.0.post.dev618.tar.gz", "codeforlife-portal"),
+        ("ChecklistDSL-0.0.1.alpha.1.tar.gz", "ChecklistDSL"),
+        ("transifex-1.1.0beta.tar.gz", "transifex"),
+        ("thespian-2.5.10.tar.bz2", "thespian"),
+        ("janis pipelines-0.5.3.tar.gz", "janis-pipelines"),
+        ("pants-1.0.0-beta.2.tar.gz", "pants"),
+        ("uforge_python_sdk-3.8.4-RC15.tar.gz", "uforge_python_sdk"),
+        ("virtuoso-0.11.0.48.b5865c2b46fb.tar.gz", "virtuoso"),
+        ("cloud_ftp-v1.0.0.tar.gz", "cloud_ftp"),
+        ("frozenordereddict-1.0.0.tgz", "frozenordereddict"),
+        ("pywebsite-0.1.2pre.tar.gz", "pywebsite"),
+        ("Flask Unchained-0.2.0.tar.gz", "Flask-Unchained"),
+        ("mongomotor-0.13.0.n.tar.gz", "mongomotor"),
+        ("datahaven-rev8784.tar.gz", "datahaven"),
+        ("geopandas-0.1.0.dev-120d5ee.tar.gz", "geopandas"),
+        ("aimmo-v0.1.1-alpha.post.dev61.tar.gz", "aimmo"),
+        ("django-migrations-plus-0.1.0.dev5.gdd1abd3.tar.gz", "django-migrations-plus"),
+        ("function_shield.tar.gz", "function_shield"),
+        ("Dtls-0.1.0.sdist_with_openssl.mingw-win32.tar.gz", "Dtls"),
+        ("pytz-2005m.tar.gz", "pytz"),
+        ("python-librsync-0.1-3.tar.gz", "python-librsync"),
+        ("powny-1.4.0-alpha-20141205-1452-f5a2b03.tar.gz", "powny"),
+        ("stp-3pc-batch-0.1.11.tar.gz", "stp-3pc-batch"),
+        ("obedient.powny-3.0.0-alpha-20141027-2102-9e53ebd.tar.gz", "obedient.powny"),
+        ("mojimoji-0.0.9_2.tar.gz", "mojimoji"),
+        ("devpi-theme-16-2.0.0.tar.gz", "devpi-theme-16"),
     ]
 
     for (filename, project) in files: