I’ll address each question individually.
(1) Actually, 2005-2011 ACS samples use the 2000 MGPUMA/PWPUMA definitions while 2012 and later ACS samples use the 2010 definitions. This is the case for both MIGPUMA1and PWPUMA00.
(2) The differences between these codes is the reference PUMA boundaries used when constructing these variables. PUMAs (public use microdata areas) are redrawn with every 10 years with each decennial census to update and more accurately represent the geographic distribution of the US population. It takes a few years for these new geographic boundaries to be used in public use ACS data, so that is why the “new” boundaries are not implemented for a couple years after each decennial census.
This might add unnecessary complexity, but the above details apply to the ACS samples, which basically implement the long form of the census questionnaire on an annual basis. The 2010 10% sample provides responses from the short form census questionnaire from the decennial census. This being the case, the 2010 10% sample implements the 2010 PUMA definitions immediately.