Thailand would know ?. You obviously assume that Embassy/Consults communicate with Immigration which they dont. One issues Visa, One enforces whats issued, they dont discuss with each other.
Many have arrived on visa exempt while waiting for their visa, then departed Thailand to nearby country and re-entered on the visa once it was issued.
You did not need to book any flight to apply, you could have simply looked up flights and wrote the details into your application, they dont ask for proof of book and dont check. Have done this on all my visa applications, multiple TR60, OA and my OX visa
Depends also if you are happy to leave for few days and come back.
If your country passport allows, you can get 60 days on arrival then extension of 30 days leave Thailand come back get 60 plus 30 extension this gives you 2 x 90 days