The received wisdom (various weighty books), seems to be that garam masalla is added near the end of the cooking process to retain its subtle flavours as far as possibe, coriander leaf is often treated in a similar manner.
I read the 'Parker21' recipe with interest for this reason, superficaily it struck me as odd that garam M was added this early in the cooking process. I have previously mentioned that the chef of the Gatwick Tandoori did not add Garam masalla to his final dishes; but I have absolutely no idea if he added it to the base! He may well have done!
Interestingly, I once found the a piece of star anise in one of his madras's! This is interesting because this spice is often used in garam masalla (albeit usually ground up). this seems to suggest that he was including 'garamy' type ingredients in his base sauce!! Or he may have slipped them into the madras he demonstrated to me when I was not looking (unlikely I watched him like a hawk!), or possibly he usually put it in his finished dishes, but did not the day I watched him!
Interesting business this curry thing!