Flightnumbers are like busnumbers, referring to a route not a specific date or time.
When the chosen Embassy says: “shouldn't ask for the DTV visa more than 3 months before actually going to Thailand"
Then you shouldn’t apply more than 3 months before, or the Embassy will have a easy way to deny you the visa, and you will loose the 10,000+ baht visafee.
Embassy websites always override answers from google or facebook.
Look at the website of the wanted Thai embassy, or search the group for those specific Embassies
The money has to have been in the account for 0 - 6 months depending on embassy.
Best to apply in your homecountry, where they are used to see the sorts of documents originating from that country, which can make processing faster, without need for additional documentation.
And you save money not traveling to and stay in a 3. country where you don’t want to be, for weeks, waiting for visa to be approved.
Use the search option before asking questions that has been answered countless times