My guess is that LeCoultre made very nice in house Chrono movements, at the end of the 19th Century and at the beginning of the 20th Century, for pocket watches.
If you have a look at the Chrono movements for Wristwatches, at " La Grande Maison ", you will notice that they appeared, for the first time, with the LE RG Reverso Chrono, in 1996 ( Cal 829 ).
There is a hole in the " in house " Chronograph production, indeed.
Why?
This is only my guess, but maybe it is due to several factors:
1/ The UG 285 and the Valjoux 72 were reliable movements, so why thinking about an " in house " solution?
2/ Conceiving an in house Chrono movement is not an easy thing, someone even told me that it was more difficult than a perpetual calendar!
JLC is filling the gaps, nowadays, and since the 90ies:
There was no perpetual calendar wrist watch, now it is done, since more than 15 years.
Same for Minute Repeaters, since 5 years, now.
A True Manufacture has to develop the ability to produce all the horological complications, IMO.
That's what they're doing, at JLC.
Best,
Nicolas