Then it isn't the same timeline. This doesn't sound like a mistake, but an active change to it by the writers.
For all we know, TOS itself was the result of temporal meddling.
Indeed, it can be argued that in a universe where "temporal war" exists, there is no "original" timeline.
The thing that gets me about "Tomorrow..." is...man, that is one ass-ugly bridge they bombed!

(Obviously there is no real Lake Ontario Bridge anyway; they just had to make up a fake landmark so they could bomb it without causing too much distress to the home viewer.)