Yesterday an announcement from the Election Commission was published in the Royal Gazette, in which the EC defines the number of constituencies per province according to the population number of December 31 2010 and with the new number of 375 constituencies [Gazette]. As mentioned before, this reduction of constituencies from 400 to 375 does not change the number of constituencies in every province. Actually this announcement on states the number of seats in parliament for every province, only because the constituencies have been changed to be single-seated this also includes the number of constituencies. The actual boundaries of these within the provinces will be announced later, though in many cases the boundaries from 2006 can be reused, the last election with single-seated constituencies under the 1997 constitution.
Interestingly this announcement does not include Bueng Kan province, obviously because the announcement was approved for publication on March 17, whereas the province came into existence on March 23. I don't know why the announcement wasn't delayed until the province was created, but luckily the calculation with or without Bueng Kan gives completely same results, the 5 seats from old Nong Khai get split into 3 for the reduced Nong Khai and 2 for Bueng Kan, and no other province is changed. So it is up to the Election Commission to draw the actual constituencies within the area formerly covered by Nong Khai using the new province boundary as constituency boundary as well. But I am sure this announcement must get an amendment to show the new province as well.