How to track transfer of patents' ownership in Patstat

One indicator of value related to a patent may be the change of ownership. The idea is simple: if somebody is willing to buy my idea, maybe it's worty.
Ownership change can also be a way of individuating patent trolls.

In pastat applicant data may change each ediction:  "the names and addresses are taken from the most recent publication of an application. In PATSTAT we discard names for earlier publications of the same application.

E.g. if we have names for a published US application, and also for a US published grant, then PATSTAT ignores the names for the published application. If there are more than 1 publications of the grant, then only the names from the latest publication are stored in PATSTAT." [from pastat docs]

If we need an easier way to track the change of ownership we may use TLS221_inpadoc_prs data where among PRS code we may find change of ownership and the name of new owner.

Some examples are
RAP1 TRANSFER OF RIGHTS OF AN EP APPLICATION
RAP2 TRANSFER OF RIGHTS OF AN EP PUBLICATION

for EPO (in appendix I'll try to make the most complete possible list for all patent offices), being aware that field L509EP contains the names of those to whom was tranferred the property.

FI: EP 1020876 in it's legal status file shows 3 records with cange of ownership on 2003/03/19:

    AUTONETWORKS TECHNOLOGIES, LTD.
    SUMITOMO WIRING SYSTEMS, LTD.
    SUMITOMO ELECTRIC INDUSTRIES, LTD.

anyway if we look @ the application or @ the original document we find 3 owner, exactly:

    SUMITOMO WIRING SYSTEMS, LTD.
    SUMITOMO ELECTRIC INDUSTRIES, LTD.
and ----  HARNESS SYST TECH RES LTD

If we look in Patstat 201010 we find:

    AUTONETWORKS TECHNOLOGIES, LTD.
    SUMITOMO WIRING SYSTEMS, LTD.
    SUMITOMO ELECTRIC INDUSTRIES, LTD.

Eventually if in espacenet we press  + key next tot applicant name, 4 applicants pop up:
    AUTONETWORKS TECHNOLOGIES, LTD.
    SUMITOMO WIRING SYSTEMS, LTD.
    SUMITOMO ELECTRIC INDUSTRIES, LTD.
        HARNESS SYST TECH RES LTD

Making a resume:


In espacenet we find the original applicants, 
pressing +, we get all the owners, even if they do not own the patent anymore

In prs legal data we get, with events of ownership change, all the new owners (if we change only 1 owner out of 50 we will have 49 records with old owners + 1 for new owner)
Patstat always contains the last owner.

APPENDIX: partial list of ownership change status

appln_ctry		prscode1	description
AT	PD9K		CHANGE OF OWNER OF UTILITY MODEL
AT	TC9K		CHANGE OF COMPANY
BE	CH		ENTRY OF CHANGE OF NAME AND/OR HEADQUARTER AND TRANSFER OF APPLICATION,PATENT AND CERTIF. OF ADDITION OF INVENTION: CHANGE OF NAME ON REQUIREMENT
BE	CN		ENTRY OF CHANGE OF NAME AND/OR HEADQUARTER AND TRANSFER OF APPLICATION,PATENT AND CERTIF. OF ADDITION OF INVENTION: CHANGE OF HEADQUARTER REFUSED
CH	SPCP		CERTIFICATES - MODIFICATION OF FIRM
CN	ASS		SUCCESSION OR ASSIGNMENT OF PATENT RIGHT
DD	ASS		CHANGE OF APPLICANT OR OWNER
DE	8327		CHANGE IN THE PERSON/NAME/ADDRESS OF THE PATENT OWNER
DE	8127		NEW PERSON/NAME/ADDRESS OF THE APPLICANT
EP	RAP1		TRANSFER OF RIGHTS OF AN EP APPLICATION
EP	RAP2		TRANSFER OF RIGHTS OF AN EP PUBLICATION
EP	BECN		BE: CHANGE OF HOLDER'S NAME
EP	BECA		BE: CHANGE OF HOLDER'S ADDRESS
EP	BECH		BE: CHANGE OF HOLDER
EP	BE20		BE: PATENT EXPIRED
EP	ITPR		IT: CHANGES IN OWNERSHIP OF A EUROPEAN PATENT
FI	GB		Transfer of assigment of application
FI	PC		Transfer of assignment of patent
GB	COOA		CHANGE IN APPLICANT'S NAME OR OWNERSHIP OF THE APPLICATION
HK	AS		CHANGE OF OWNERSHIP
IL	HP		CHANGES IN PROPRIETORSHIP
LT	PD9A		CHANGE OF THE GRANTEE
LT	PC9A		TRANSFER OF PATENTS
MD	PD4A		CHANGE OF PROPRIETORSHIP
NL	CD		TRANSFER OF RIGHTS (LAID OPEN PATENT APPLICATION)
NL	CNR		TRANSFER OF RIGHTS (PATENT APPLICATION AFTER ITS LAYING OPENFOR PUBLIC IN
NZ	ASS		CHANGE OF OWNERSHIP
PT	PC4K		TRANSFER OF ASSIGNMENT (UTILITY MODEL)
PT	PD4K		CHANGE OF PROPRIETORSHIP (UTILITY MODEL)
PT	PC3K		TRANSFER
PT	PD3K		CHANGE OF PROPRIETORSHIP
PT	PD3A		CHANGE OF PROPRIETORSHIP
PT	PD4A		CHANGE OF PROPRIETORSHIP