I think you are a bit over yourself here. I can asset with surety that I had access to Toyota Crown/Corona/Cresta/Corolla/Hiace/Hilux/Land Cruiser/Coaster parts like a kid in a candy store - I could get used parts of "model specific code" delivered to my place of business from outside of Pakistan with no problems in very short time. I could get a plethora of other brand car parts too, all tested and working.
Anyway thats not the discussion.
What we are looking at here is that you said a gray market car came in with severe driveability problems. The toyota dealership gave it full marks and A OK (very odd or the dealership should actually close their doors) - then you say that the owner did not want to spend any reasonable amount of money to repair his "luxury" car because according to him the total cost of repairs are OVER the cost of USED ENGINE - you also report that the injectors were bad, the Fuel pump control module was bypassed etc.etc.
Such customer should never ever be entertained in any respectable workshop.
Then you say that the car was tuned to perfection by an add on box that fooled the ECU and somehow the "clogged" fuel injectors started to work and the engine started to work properly - that too a direct injection one - its a remarkable feat no doubt but I have my concerns too - I have worked on some engine control systems ranging from these passenger cars like toyota crowns to heavy machinery that costs multiple of millions in USD. machines big enough that they take 800 litres engine oil. Uptil today I have not seen any driver unit capable of reworking a clogged injector to the extent of the engine running good after a complete failure run. You also mention that you go to 16:1 AFR and still face no knock on regular pump petrol used in Pakistan. high AFR on high CR engine in a simple wet manifold otto cycle gasoline engine is bad - its till the range of misfire - in a direct injection I know it can do that on overrun or cruise as the fuel spray can absorb the heat from the charge air - but still it has to go back to 14:1 to keep NOx down and to keep knock at bay.
The last bit is what is very strange - thats the major question here. I posted about LTFT to which you have not replied correctly, any correct working ECU will work the engine to be at 0.0 STFT and a range of +/-5% LTFT is considered acceptable - it keeps the duty cycle of the injectors in mid.
Its pretty nice what you have - if you say it works, but instead of using customer's cars why not make a test rig (you should have a lot of engines lying around if you are the sole supplier of Toy Crown parts) then do control and run tests like any proper lab would do.