HP-35 Serial Number Question

[Corvallis Bill]

Hi,
I have the 35 with a raised bump on the "5" button, signifying it is rather early in its evolution.
The ser no is 1143A 41k and from what I read, that indicates it was manufactured in 1971, in the US.
So far, all of the articles I've read about this series says they were "first released in 1972", so my question is why wouldn't this one be serialized with the 1200xxxxx designation? Was it an earlier production unit?
I know there are others with the 1143A ser no so wouldn't it then stand to reason that the first release would have been in 1971..? Any historians out there with the answer..??
Thanks..Bill (a.k.a. Corvallis Bill).