The source for the 84,000 figures seems to be these verses from Thag17.3:
Dvāsīti buddhato gaṇhiṃ,
dve sahassāni bhikkhuto;
Caturāsītisahassāni,
ye me dhammā pavattino.
I learned 82,000 from the Buddha,
And 2,000 from the monks;
These 84,000
Are the teachings I have memorized.
https://suttacentral.net/en/thag17.3/1.1018-
Mind that Ananda is above recorded to have heard 82,000 and 2,000 dhammas from Buddha and the bhikkhus, respectively.
While it makes sense to translate dhammā as “teachings” here it may not be necessarily correct to expect tha 84,000 recorded discourses (suttas / sutras) would be found in the Tipitaka / Tripitaka.
It is interesting how over the time this figure has been re-quoted to mean things like 84,000 doors to awakening, 84,000 antidotes for mental afflictions, etc… 