They are in data\text\historic_events.txt
This one is "Welcome"
{PRESENTAZIONE_TITLE}
{PRESENTAZIONE_BODY}
And this one is "Extra Costs"
{COSTI_SUPPLETIVI_TITLE}
{COSTI_SUPPLETIVI_BODY}
In the English text provided by the official BC team, they look like this:
However there is no sense that the "welcome title" shows "Welcome to Bellum Crucis 6.2!" in Bellum Crucis 7, obviously the developer or the translator forgot to update.
So in my case I simply modify it as: {PRESENTAZIONE_TITLE}Welcome to Bellum Crucis 7.0!