Nothing is being made up. You can enter Thailand with a Visa or for many countries, Visa Exempt (no visa required).
Upon arrival, Immigration places a stamp in the passport showing the permission to stay period which is based on the type of entry (Visa or Exempt). These are two separate things. To extend your stay you apply to extend your permission to stay not your visa. I entered Thailand over 20 years ago on a Non-Immigrant O Visa receiving a 90 day permission to stay. I applied to extend that stay for one year for purpose of retirement. For the past 20+ years I annually go to Immigration and file a TM.7, Application for Extension of Temporary Stay in the Kingdom.
The Pattaya City Expats Club has an extensive section re entering Thailand, extending one's stay, and other Thai Immigration requirements at https://pcec.club/Thai-Immigration. The difference is also noted on this Thai Embassy's website - https://helsinki.thaiembassy.org/en/publicservice/information-about-visa-and-validity-of-stay-permit?page=5f49f4a199a85e260f4278de&menu=5d80876d15e39c3354007bb1