Well from what i know now i suggest 2 options to get out of amnesty no stamp visa situation.
Option 1. Present letter show on my post to your IO, explain to them why you weren't able to extend your visa sooner. My friend told IO that he wasn't able to do the border run since the shut down and the 1st government announcement caused confusion because it say no need to extend the visa. The 2nd announcement say amnesty clearly that everyone need to get on a valid visa before 26 September 2020, but according to the law he cannot apply or convert to any type of visa from overstay (amnesty no stamp). So he need the stamp in order to apply or extend his Non-B work visa before Sept 11th as to have valid visa after the amnesty end. This stamp can be obtain with no cost.
Option 2. Request unable to travel due to Covid19 letter from your embassy and present to IO accordingly. I called 1178 last Friday to ask about this, and was inform that foriegner can get the visa stamp for 30 days unlimited time as long as they can present letter from the embassy. There are few report on people getting visa stamp that will expire Sept 11th and Sept 16th and was asked to return again with same letter to get another 30 days. This stamp will cost you 1,900.00 Baht each time.
I was actually surprised myself, i thought he would get normal stamp that say nothing on his passport just like the one that expired on 28 April
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. I told him to find out from the immigration officer whether he can apply for Non-B in thailand and what documents will he need. That's when they told him you already have Non-B and guide him to get queue for business visa extension after his old stamp was transferred to new book. (he have a new passport so he did transfer his stamp first.)
He was told by the immigration officer themselves that he already have Non-B visa. More so, it say on his stamp 'ธุรกิจ' which mean business. But yeah, we are preparing documents to get his visa extension hopefully before 11 Sept 2020.