Update StandardizationGuidelines.md

Author: nataled

docs/StandardizationGuidelines.md

@@ -33,7 +33,11 @@ GO TO: [Technical Considerations](#technical-considerations) | [Content-Con
 - Preferred source for imported terms (no tracker item)
   - Imported terms SHOULD be drawn from the ontology that is the preferred source for the term. The preferred source is usually the ontology with the same ID space as the term, but it can instead be the ontology that currently maintains the term. Importing a term from a secondary source is not recommended because there is no guarantee that the secondary source has the most up-to-date term information, and thus drawing from the original would avoid possible conflicts due to term divergence.
 - Whole ontology imports ([tracker item](https://github.com/OBOFoundry/OBOFoundry.github.io/issues/2769))
-  - Unless necessary, an entire ontology SHOULD NOT be imported if only a subset of terms is needed. To import terms on an individual basis, [ROBOT 'extract'](https://robot.obolibrary.org/extract) and [OntoFox](https://ontofox.hegroup.org/index.php) are useful tools.
+  - Unless necessary, an entire ontology SHOULD NOT be imported if only a subset of terms is needed. To import terms on an individual basis, [ROBOT 'extract'](https://robot.obolibrary.org/extract) and [OntoFox](https://ontofox.hegroup.org/index.php) are useful tools. Notable exceptions are imports of small ontologies that provide upper level structure or useful sets of properties:
+    - BFO (Basic Formal Ontology) or COB (Core Ontology for Biology and Biomedicine) are upper level ontologies used to harmonize multiple OBO Foundry ontologies under the same hierarchy.
+    - OMO contains commonly used annotation properties.
+    - RO Core contains the most commonly used relations.
+
 
 ### Release Considerations