Suppose we did (for the first time) have a TOE that theoretically predicts all the experimental results to date on all sclaes of size.
However two things are still in question:
1. How accuately does it predict everything (that have been experimentally carried thus far) at all scales?
2. How accurately can it explain or predict further phenomena ?
Both questions will challenge the TOE and forever modify it to the point where some time after the first TOE is invented, the latter ones may be very different to the first one i.e use entirely different mathematics. So in that way even if we have a TOE, it is not literally the theory of everything.