OpenAtlas

Turning this into a question because it doesn't affect the functionality of OpenAtlas or the CIDOC CRM validity of data produced with OpenAtlas in any way.
That being said, you are correct that P3 is in the CIDOC specification but not in OpenAtlas. It could have been a bug, so thank you for reporting.

The reason P3 isn't in OpenAtlas is that it's one of these "special" cases. From the specification:

4. RDF does not support properties of properties, therefore, users may create their own
   subProperties for CRM properties that have a type property such as "P3 has note":
   Instead of P3 has note (P3-1 has type : parts description) declare
   <rdf:Property rdf:about="P3_parts_description">
      <rdfs:domain rdf:resource="E1_CRM_Entity"/>
      <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Literal"/>
      <rdfs:subPropertyOf rdf:resource="P3_has_note"/>
   </rdf:Property>

There are some other properties we ignore, you can look them up in the OpenAtlas CIDOC parser script where they are defined at the top: https://github.com/craws/OpenAtlas/blob/main/install/crm/cidoc_rtfs_parser.py
We don't import them because of technical reasons, e.g. they are missing some definitions that "normal" properties have and the import script would have troubles to deal with them. E.g. they have no defined range but this is a foreign key in our database that can't be empty.
For us it is more important that the subset of entities and properties that we use have structural integrity than mapping the CIDOC CRM specification as whole.
Feel free to ask more, I'm sure that e.g. Stefan can explain this a lot better. In case this already answers it you can close this issue.

Thank you again for reporting, this definitely could have been a bug.