No, I think it is the right place.
Sending frames to DRS for rework or store them for long time (and likely rework) in XFW with engines is quite hard to explain by engine issues.
Your high trust engine argument might be good for 10 frames, but XFW lacks much more. They are still in 88xx/89xx and TLS now reached 91xx. And the 88xx and 89xx are all types.
There are some unallocated MSN around 9000 and 9100, so I already think XFW removed some to close the gap or prevent it to increase.
There are frames undelivered all the way down to MSN8140.
If we look at undelivered frames below 8900, 37 all together.
We find all kinds of frames.
A321, 22: 15 ACF, 9 LEAP + 6 P&W, 5 non ACF, 1 LEAP + 4 P&W, 1 A321ceo
A320, 16: 14 A320neo, 4 LEAP + 10 P&W. 1 A320ceo
A319, 1: 1 A319neo LEAP
Frames below 8700
In the above there are 4 frames for LATAM all A320neo P&W MSN8140 8172 8531 8635,
1 frame for Astana an A321 P&W MSN 8277,
1 frame for GoAir an A320 P&W MSN 8445,
2 frames intended for Primera, both ACF LEAP MSN 8547 8602,
and 1 Frame for Arctic tern, the A319neo LEAP MSN 8612.
All this frames, 9, are below 8700 and I assume mostly different problems not connected to production problems, account for why they are still there in XFW.
Frames between 8700 and 8800.
MSN8753 an A321neo P&W for Vietnam Airlines not flown yet
MSN8757 an A320neo P&W for GoAir, FF 01.07.2019
MSN8773 an A321neo ACF LEAP for TAP not flown yet
MSN8774 an A320neo ACJ LEAP private owner
MSN8776 an A321neo P&W for Sichuan Airlines
MSN8785 an A320neo P&W for GoAir, not flown yet
I assume the 6 frames above can have all other explanations than XFW production problems.
Frames between 8800 and 8900
MSN8800 an A321neo ACF LEAP for American Airlines
MSN8814 an A321neo ACF P&W for Lufthansa
MSN8822 an A321ceo for Delta
MSN8829 an A321neo LEAP for Alaska Airlines
MSN8834 an A321neo ACF LEAP for AA
MSN8836 an A320neo P&W for Sichuan Airlines
MSN8837 an A321neo ACF P&W for Astana
MSN8839 an A321neo ACF P&W for Air New Zealand FF 02.07.2019
MSN8844 an A320neo P&W for Volaris not flown yet
MSN8849 an A321neo P&W for Sichuan Airlines
MSN8851 an A320neo LEAP for China Southern not flown yet
MSN8861 an A321neo ACF LEAP for Air Arabia not flown yet
MSN8863 an A320neo LEAP for Pegasus FF 04.07.2019
MSN8864 an A320neo P&W for Indigo not flown yet
MSN8873 an A320neo P&W for Sichuan
MSN8882 an A321neo ACF P&W for Wizz not flown yet
MSN8887 an A321neo ACF LEAP for Air Lingus, not flown yet, picture with engines 24.06.2019
MSN8889 an A320neo LEAP for Avianca FF 18.06.2019
MSN8892 an A320ceo for Peach, not flown yet, I have not seen a picture with engines.
MSN8893 an A321neo ACF P&W for JetBlue, not flown yet
MSN8897 an A321neo ACF LEAP for Air Arabia, not flown yet
MSN8898 an A321neo ACF LEAP for AA not flown yet.
It would be interesting now sciing, if you could point to me to the frames above, where you are sure that production problems other than engine delays is the proper reason for late delivery. Excluding the frames where the buyer is responsible for late delivery.
best regards Mjoelnir