Considering Pakistan had to fight tooth and nail for basic documentation created by CAC to get the ability to integrate third party systems such as radios, EW and health monitoring systems - it does now have access to the majority of the aircraft’s mission computer and bus architecture source.
However, your assertion that the source code is needed for optimal weapons performance is wrong.
Modern integration frameworks are designed specifically to avoid needing access to a weapon’s or aircraft’s proprietary software.
A weapon’s internal algorithms (like guidance or fuzing logic) operate autonomously once the correct data is provided via these interfaces. As long as the aircraft feeds accurate target coordinates, attitude, and timing signals, the missile performs as designed.
The Indian Su-30MKI fires Israeli and French weapons, and Eurofighter Typhoon loads Israeli decoys and none of these required full software source code but relied on ICDs and modular integration software.
Easy to use and useable are not reliant on source code - they are related to seamless mission computer integration, pilot interface, accurate threat symbology, and smooth datalink updates and not necessarily algorithm-level integration.
The limiting factor is often documentation and interface access, not inaccessible source code. If the weapon manufacturer supplies a full Interface Control Document, you can integrate effectively even with a closed “black box.” Claiming it was "embarrassing" because Level 4 access wasn’t granted ignores that nearly all mixed-origin fighter integrations (including Western ones) operate effectively at Level 3 or 3.5. If Azerbaijan has not been able to integrate weapons yet it can be due to limited cooperation from OEM, inconsistent software documentation, or rushed integration timelines.
