OP reporting back: at some point in the past 21 hours the missing flights and associated miles magically appeared in my and my wife's accounts.
Thank you!
Excellent service from the social media team and the tip is appreciated,
Oliver2002. I've now requested assistance with another issue (an erroneous mileage
credit -- not a problem of LH's making this time, but their help is needed to resolve it).
It's good to get my issue resolved, but still frustrating that the normal channels often function so poorly -- if an empowered human being had actually read any of my four (!) letters and spent 20 seconds checking the ETKT record, the file would have been closed months ago. I know from past experience and many other reports that this isn't exactly unusual -- making it a crazy waste of LH resources as well as a source of great frustration for customers.