Phil,
I hear what you say with regards to a generic spice mix but like the base, this is just a 'foundation' ingredient. Yes, it will leave it's 'signature' on a range of dishes from one particular establishment but it is all the other additions that change the actual flavour!
However, the variables/permutations are endless for example;
200ml base
garlic and ginger paste, 50/50
2 tsp spice mix
1 tsp methi
1 tbs tomato puree
Will taste quite different to:
300ml base
garlic and ginger paste, 70/30
1 tsp spice mix
1.5 tsp methi
2 tbs tomato puree.
Same ingredients, just combined quite differently! I know some may disagree but for the most part BIR curries are 'formula' dishes. A bit more of this, a little less of that, add this, leave that out and so on, all produce a different dish.
Even varying the length of time you take to cook your dish will alter the taste somewhat, even if using the same ingredients. Hopefully, our BIR chefs are skilled enough to play around with the combinations and produce very good dishes, albeit with their special stamp on the dish which could be attributed to their 'secret' spice mix?
Just my thoughts

Ray
