Receiver says Underwood but serial number says otherwise

I purchased an M1 from a friend. The receiver is marked Underwood. The barrel is also marked Underwood and has a date stamp of 1-43. The front sight is marked with a "U" and the trigger group is marked "Inland". Now here is what I am trying to find out. The serial number on my rifle is 1,870,8XX. I looked on line and one website says Irwin-Pederson/Saginaw (S'G") had a serial number range of 1,762,520 through 1,875,039 and another website says that Quality Hardware & Machine Co had a serial number range of 1,850,040 through 1,907,519 (July 1943 - Aug. 1943). So who made the rifle I have? My serial number falls between both of these ranges and it does not fall into any of the Underwood Elliott-Fisher serial number ranges. Thanks in advance for information.

I guess it proves you can not 100% believe all these websites and lists. Perhaps there were over runs as with Garand's?

I would ask you to check the receiver again. Look to see if the serial number isn't 2.8 and not 1.8. Also look real close at the date on the barrel to see if there isn't a 1 in front of the one you did see. A lot of times they can be real faint.