so from my understanding since you have used your extension with your last entry stamp on January 31st you can't get an extension when the amnisty runs out.
I am sure that they will be giving a grace period of 7-14 days(hopefully longer) to make arrangements to get your visa sorted to stay in country or to leave with no penalties or repercussions.
Past that GUESS..... You are really needing the wait and see approach. I know it sucks.
I hope you came on a 90day visa with a 30 day extension that took you to a valid visa date on the 27th of March or after.
If you didn't have that your are on overstay and are going way over the 90days and will be banned for at least a year. Plus fine playable on exit is you goto jail.
where is your information that is stating the entry stamp is expired? The amnesty extended the expiration date on the stamp. If it didn't everyone would be on overstay and here illegally according to the rules.
You even stated it was designed to give people time to leave or work on getting the correct long term visa.
Do you work for immigration or a reputable visa agency or are you like everyone else throwing out speculation of your opinion.