Thanks. The numbers are imprinted at the factory, and can be a good way to verify that your discs are genuine by matching them with known genuine numbering patterns. The Z4 , 4R2SL, and C30R are present on my 4x Panasonics as well. The 6x Panasonic stamper shows 6R2SL.
In truth, the high quality of your burn speaks even louder to verify that they are the real thing :).
As the only two BD-R manufacturers that are keeping all manufacturing in-house and using high-end Japanese machinery, materials, and disc designs and offering 50+ year longevity testing results, I have a high level of confidence in either Panasonics or Falcons.
I notice that the moderators have tried(unsuccessfully) to move our discussion out of the test thread area. I welcome these discussions, and please continue to post your burn results in the test threads. But we must try to stick to the "no discussions in the test threads" format that the forum has chosen. In the future, simply click on the "post new thread" button in the main blank media forum and start a discussion there, referencing your posted scan in the test thread if you'd like :).