Not usually. They usually do that for the 30-day standard extension. But for the Covid extension, most have reported that the 60 days started from the end of their existing stamp.
Which office did you go to?
Well, to be fair it is in vogue to run a "subscription-based" business model these days.
Pay-as-you-go is so "old school". https://www.nationthailand.com/in-focus/40005603