I 've seen many people strugling to understand why a specific gam file in one gamma card plays fine but in another it doesn't play, why some cards lock and some not etc etc (especially for the n@va gr33k package).
While I don't know for sure, since I don't have the gamma os, I've come to some conclusions.
Conclusion #1: gamma os + gam file is not a real subscription card. For example, if it was, the provider could easily check the serial in the card and block specific serial. However this does not happen. We've seen a gam file to give different serials in different gamma cards. Also, there is no real subscription card for n@va that decodes all channels (Rxx channels too).
Conclusion #2: Since a gamma os + gam file is not a real subscription card, it is clear to me that gamma os is actually a hack in the irdeto algorithm, allowing to get channel updates even without a valid subscription. The serial displayed is actually fake. That's why the providers have problems to shut down the card.
Conclusion #3: It seems to me that the above "hack" is not without flaws. Different versions of the card having different versions of the hack, act differently. Maybe the providers have found some sort of ECM/EMM commands that make the "hack" operate badly and thus, locking the card. There is no other explanation to the fact that you program a card with a gam file, it works for some days and then it fails, but if you program it again, it works again.
Conclusion #4: The gamma irdeto hack has not yet been understood by irdeto themselves. That's why they don't change cards to newer versions, that's why they can't close gam files that operate for months now, that's why ADD package is switching to viaccess and dumps irdeto. Also, it seems that newer versions of irdeto are also hacked (gamma is 4.1 but kebap is 5.2 i think).