Be careful
If you are going to create your own system, or rely on someone else's for that matter, be sure to read the fine print in the ATF ruling cited above ...
The system must retain any correction of errors as an entirely new entry, without deleting or modifying the original entry (e.g., macro created to track changes). Alternatively, the system may allow for entries in a “notes” column to explain any correction and/or track changes (i.e., what was changed, who made the change, why the change was needed). ATF suggests that the recordkeeping system be capable of blocking fields from correction (e.g., protect workbook function).
and ...
The system must back-up the firearms acquisition and disposition records on a daily basis to protect the data from accidental deletion or system failure.
and, finally ...
All laws, regulations, policies, and procedures applicable to the paper form of the firearms acquisition and disposition records also apply to electronic versions. Licensees are not required to use an electronic acquisition and disposition record, and may continue to use a paper record in the format prescribed by regulation. Licensees are reminded of their responsibility to ensure accuracy and completeness of all of their required records.
Also, to be clear, MyGunDB is not a CMP application. It is affiliated with the CMP in that portions of the proceeds go to support the CMP. NM Collector Software has the same affiliation with the CMP. Here is a link to the "CMP apps" page:
http://thecmp.org/communications/app/