I would like to say that I find something missing in the sentences that you have mentioned.
firstly the first part of the sentence should be like:
I couldn't have reached the meeting on time (as here the past perfect tense is being used)
and secondly it is 'early train' not 'earlier train'.
and the sentence would appear something like this:
I couldn't have reached the meeting on time, if I hadn't caught an early train.
It is just my opinion. You may take help from others.