Too many mistakes and revised again

Yes, the safe deadline for you to apply for a H-1b transfer is just a couple of weeks after your last regular pay check. You should have negotiated with your previous employer to put you on their payroll as long as possible by using severance package, or have filed a bridge applcation after your last regular paycheck. My advice is, if you get an offer tomorrow, consult with a lawyer (or company lawyer) to see if your H-1 transfer is approvable or you can just file a new H-1 application and leave the country to grab the H1 when it is approved.