diff --git a/hytek/hy3/file.py b/hytek/hy3/file.py
index 15c5869..feb11ed 100644
--- a/hytek/hy3/file.py
+++ b/hytek/hy3/file.py
@@ -1,7 +1,7 @@
 import zipfile
 from logging import warning
 
-from .records import Hy3Record, RECORD_TYPES
+from .records import Hy3Record, Hy3RecordGroup, RECORD_TYPES
 
 
 __all__ = ("Hy3File",)
@@ -32,7 +32,6 @@ def read(self) -> None:
         if self.file is None:
             self.file = open(self.filepath, "rb")
         parents = []
-        last_record = None
         records = []
         data = self.file.read()
         for i, line in enumerate(data.splitlines()):
@@ -46,33 +45,31 @@ def read(self) -> None:
                 records.append(record)
                 continue
 
-            if last_record:
-                # Hy3RecordGroup
-                if last_record.record_type[0] == record.record_type[0] and last_record.record_type[1] < record.record_type[1]:
-                    last_record = last_record.add_to_group(record)
-                    if parents:
-                        parent = parents[-2]
-                        parent.children[-1] = last_record
-                        parents[-1] = last_record
-                    else:
-                        parents.append(last_record)
-                        records.append(last_record)
-                    continue
-            last_record = record
-
+            done = False
             while parents:
                 parent = parents[-1]
-                if parent.record_type >= record.record_type:
-                    parents.pop()
-                else:
+                if parent._child_allowed(record):  # child record
+                    parent.append_child(record)
+                    parents.append(record)
+                    done = True
                     break
-            if parents:
-                parent = parents[-1]
-                parent.append_child(record)
-                parents.append(record)
-            else:
+                elif parent._group_allowed(record): # group record?
+                    group = parent.add_to_group(record)
+                    parents[-1] = group
+                    # get the group's parent
+                    # should be the record immediately before
+                    # the group record
+                    group_parent = parents[-2]
+                    # update children of the group's parent
+                    group_parent.children[-1] = group
+                    done = True
+                    break
+                parents.pop()
+            if not done:
                 records.append(record)
                 parents.append(record)
+            pass
+
         self.records = records
         self.file.close()
         self.file = None
diff --git a/hytek/hy3/records.py b/hytek/hy3/records.py
index 3cbb029..a240e34 100644
--- a/hytek/hy3/records.py
+++ b/hytek/hy3/records.py
@@ -30,6 +30,16 @@
 )
 
 
+ALLOWED_CHILDREN = {
+    "A": ["B"],
+    "B": ["C"],
+    "C": ["D", "F"],
+    "D": ["E"],
+    "E": ["G", "H"],
+    "F": ["G", "H"],
+}
+
+
 class Field:
     def __init__(self, *, name: str, length: int, type: Callable[[str], Any] = str):
         self.name = name
@@ -46,9 +56,12 @@ def __init__(self, *records: Type[Hy3Record]):
     def __repr__(self):
         return f"<Hy3RecordGroup group_type={self.group_type} records={self.records}>"
 
+    def _child_allowed(self, child: Hy3Record | Hy3RecordGroup) -> bool:
+        return child.record_type[0] in ALLOWED_CHILDREN.get(self.record_type[0], [])
+
     def append_child(self, child: Hy3Record | Hy3RecordGroup) -> None:
-        if child.record_type < self.group_type:
-            raise Exception("Child record type is less than parent")
+        if not self._child_allowed(child):
+            raise Exception("Child record type is not allowed in this parent.")
         self.children.append(child)
 
     def remove_child(self, child: Hy3Record | Hy3RecordGroup) -> None:
@@ -74,9 +87,16 @@ def to_json(self) -> dict:
     def record_type(self) -> str:
         return self.records[-1].record_type
 
-    def add_to_group(self, record: Type[Hy3Record]) -> Self:
+    def _group_allowed(self, record: Type[Hy3Record]) -> bool:
         if record.record_type[0] != self.group_type:
-            raise Exception("Record type does not match group type")
+            return False
+        if int(record.record_type[1]) <= int(self.records[-1].record_type[1]):
+            return False
+        return True
+
+    def add_to_group(self, record: Type[Hy3Record]) -> Self:
+        if not self._group_allowed(record):
+            raise Exception("Cannot group records")
         self.records.append(record)
         return self
 
@@ -108,9 +128,12 @@ def __getitem__(self, item: str) -> Any:
     def __setitem__(self, item: str, value: Any) -> None:
         self.data[item] = value
 
+    def _child_allowed(self, child: Type[Hy3Record | Hy3RecordGroup]) -> bool:
+        return child.record_type[0] in ALLOWED_CHILDREN.get(self.record_type[0], [])
+
     def append_child(self, child: Type[Hy3RecordGroup | Hy3Record]) -> None:
-        if child.record_type < self.record_type:
-            raise Exception("Child record type is less than parent")
+        if not self._child_allowed(child):
+            raise Exception("Child record type is not allowed in this parent.")
         self.children.append(child)
 
     def remove_child(self, child: Type['Hy3Record']) -> None:
@@ -124,9 +147,16 @@ def print_tree(self, depth: int = 0) -> None:
         for child in self.children:
             child.print_tree(depth + 1)
 
-    def add_to_group(self, record: Type[Hy3Record]) -> Hy3RecordGroup:
+    def _group_allowed(self, record: Type[Hy3Record]) -> bool:
         if record.record_type[0] != self.record_type[0]:
-            raise Exception("Record type does not match group type")
+            return False
+        if int(record.record_type[1]) <= int(self.record_type[1]):
+            return False
+        return True
+
+    def add_to_group(self, record: Type[Hy3Record]) -> Hy3RecordGroup:
+        if not self._group_allowed(record):
+            raise Exception("Cannot group records")
         group = Hy3RecordGroup(self, record)
         return group