diff --git a/nnpdf_data/nnpdf_data/commondata/NNPDF_FIATLUX_NOTFIXED/kinematics.yaml b/nnpdf_data/nnpdf_data/commondata/NNPDF_FIATLUX_NOTFIXED/kinematics.yaml
new file mode 100644
index 0000000000..24265f2192
--- /dev/null
+++ b/nnpdf_data/nnpdf_data/commondata/NNPDF_FIATLUX_NOTFIXED/kinematics.yaml
@@ -0,0 +1,3 @@
+bins:
+- x:
+    mid: 0
diff --git a/nnpdf_data/nnpdf_data/commondata/NNPDF_FIATLUX_NOTFIXED/metadata.yaml b/nnpdf_data/nnpdf_data/commondata/NNPDF_FIATLUX_NOTFIXED/metadata.yaml
new file mode 100644
index 0000000000..34fa22e607
--- /dev/null
+++ b/nnpdf_data/nnpdf_data/commondata/NNPDF_FIATLUX_NOTFIXED/metadata.yaml
@@ -0,0 +1,44 @@
+setname: NNPDF_FIATLUX_NOTFIXED
+
+version: 1
+version_comment: Meta-dataset to allow for the evolution of the photon structure function
+
+nnpdf_metadata:
+  nnpdf31_process: null
+  experiment: null
+
+implemented_observables:
+- observable_name: F2
+  observable:
+    description: F2 structure function
+  process_type: DIS
+  ndata: 1
+  plotting:
+    dataset_label: ''
+  kinematic_coverage: []
+  kinematics:
+    variables:
+      x:
+        label: $x$
+    file: kinematics.yaml
+  theory:
+    FK_tables:
+    - - FIATLUX_DIS_F2
+  data_uncertainties: []
+- observable_name: FL
+  observable:
+    description: F2 structure function
+  process_type: DIS
+  ndata: 1
+  plotting:
+    dataset_label: ''
+  kinematic_coverage: []
+  kinematics:
+    variables:
+      x:
+        label: $x$
+    file: kinematics.yaml
+  theory:
+    FK_tables:
+    - - FIATLUX_DIS_FL
+  data_uncertainties: []
diff --git a/validphys2/src/validphys/commondataparser.py b/validphys2/src/validphys/commondataparser.py
index a98151c174..6ed4779250 100644
--- a/validphys2/src/validphys/commondataparser.py
+++ b/validphys2/src/validphys/commondataparser.py
@@ -433,7 +433,7 @@ def check(self):
         has been read, the observable selected and (likely) variants applied.
         """
         # Check whether the data central or the uncertainties are empty for a non-positivity/integrability set
-        if not self.is_lagrange_multiplier:
+        if not self.is_nnpdf_special:
             if self.data_central is None:
                 raise ValidationError(f"Missing `data_central` field for {self.name}")
 
@@ -503,8 +503,9 @@ def is_integrability(self):
         return self.setname.startswith("NNPDF_INTEG")
 
     @property
-    def is_lagrange_multiplier(self):
-        return self.is_positivity or self.is_integrability
+    def is_nnpdf_special(self):
+        """Is this an NNPDF special dataset used for e.g., Lagrange multipliers or QED fits"""
+        return self.setname.startswith("NNPDF")
 
     @property
     def path_data_central(self):
@@ -518,7 +519,7 @@ def load_data_central(self):
         pd.DataFrame
             a dataframe containing the data
         """
-        if self.is_lagrange_multiplier:
+        if self.is_nnpdf_special:
             data = np.zeros(self.ndata)
         else:
             datayaml = _quick_yaml_load(self.path_data_central)
@@ -545,7 +546,7 @@ def load_uncertainties(self):
         pd.DataFrame
             a dataframe containing the uncertainties
         """
-        if self.is_lagrange_multiplier:
+        if self.is_nnpdf_special:
             return pd.DataFrame([{}] * self.ndata, index=range(1, self.ndata + 1))
 
         all_df = []