Last Day of Enforceability for Patent 4,xxx,xxx

Today marks the end of the four millions.

U.S. Patent No. 4,997,100 Unitary biological specimen processing apparatus Inventor: Peter P. Dudek Issued: March 5, 1991 Filed: August 31, 1990 Abstract: A Unitary biological processing apparatus for processing specimens therein is described wherein a perforated receptacle member with two arc shaped abutment means and a third hook shaped abutment means is attached through a frangible hinge portion to a perforated lid member with two arc shaped detent means at the two edges of the lid member which are perpendicular to the lid member edge extending along the hinge portion, and a third detent means engageable with the hook shaped abutment means. When the lid member is swung about the hinge the arc shaped engagement means become engaged even before the lid member mates against the receptacle member and the two arc shaped engagement means provide with the third engagement means a three-point lock of the lid member onto the receptacle member

You can check for yourself, or you can take my word for it: any other patent under 5,000,000 is either: a) 20 years past its earliest priority date; or b) expired for failure to pay maintenance fees. (And every patent under 5,000,000 is more than seventeen years past issuance.)

Challenge: When will the last of the 5,000,000s expire? I suspect that PTE (which was not applicable to the 4,000,000s) may cause major headaches in determining the answer.