I have a Non-B visa, multiple entry, expires on Oct 24, 2016. 

My last border bounce was Sept.24, 2016 and now stamp is good until Dec.22, 2016.

My lawyer tells me I do not need to renew my Non-B until Dec.22, 2016 even though it expires on October 24/2016.

Can you please confirm if true. Thank you.

True! 

 

Also

If you make an exit/entry just prior to the visa expiring you will be granted another 90 day entry.

 

 

Your visa cannot be "renewed" - you can either apply for an extension of your permitted stay in Thailand or you can leave Thailand and obtain another visa.  To extend you current stay in Thailand, you must qualify for an extension under one of the categories listed in Police Order 327/2557 (see here).  If you do not qualify (or prefer not to apply for an extension), you must leave Thailand before your current permitted stay expires (December 22).  You could then apply for another visa in another country, assuming you have the appropriate paperwork to do so.  Note that multiple entry Non-Imm "B" visas are very difficult to obtain in the SEA region.

 

As Fithman mentioned, you could leave and return one more time before your existing visa expires on October 24.  You would then have permission to stay for 90 days from that entry.

Thank you for your replies..

Do not confuse the validity of your visa (when you can use it to enter Thailand) with your permission to stay (when you must leave Thailand or apply for an extension). Your lawyer is correct that expiry of the visa has no bearing on your permission to stay.