I understand. Just going on what my employer's HR was told my Immigration at Chaengwattana when we queried whether we needed to renew his Extension. Maybe they just wanted the 1,900 baht!
I guess you're not extending at the main Immigration office in Bangkok, as they have extended my 3 year old's Extension twice now. Or maybe extending a visa is different. Either way, it was recommended to me that I should keep his immigration status legal, even though there is no fine or ban, as he would still get stamped as overstaying in his passport.