In the last two month the upgrade of 200 TAO to municipalities was decided, so even in just this short time nearly twice the number of the whole fiscal year 2007. And even in 2007 it was an extraordinary high number of upgrades, the years before it was always less than 10. After thinking about this, I remembered that the TAO were all created in four batches in 1995 to 1999. Thus last year the 1995 creations had their 12th anniversary, this year it's the 1996 creations. Thus with a 4 years term for the TAO council, this year the TAO created in 1996 have to held elections anyway, thus it would be more economically to do the municipality upgrade at the end of the TAO term, as after the upgrade a new election needs to be done anyway. While this does not explain way so many TAO become eligible for the upgrade now, at least it explains why so many upgrade in this two years. If my guessing is right, it'd mean that 2009 will see even more upgrades, as 1997 was the year with the biggest number of TAO establishments.
Or is the big number of upgrades related with the drop of the population density requirement? At the time I researched for the thesaban article on Wikipedia, I found a reference that for a subdistrict municipality a population density of 1,500 per km² is mandatory - not only most of sanitary district upgraded in 1999 did not match this, but also almost all the TAO upgraded now neither. But I have no idea when (and if) this requirement was actually dropped.
In Nakhon Ratchasima province it now has more than 70 municipalities, which now makes the geocode system mentioned earlier impossible. As the province already has 32 districts, now the municipality geocodes descending from 3099 and the district codes starting from 3001 must overlap already. And there even was at least one code in between (3049) used for a Sakha Tambon. So for the municipalities they have to change the way the geocodes get assigned. I have no idea if or how this was or will be done, I haven't found much about the codes for the municipalities on the web so far, even trying my luck with googeling Thai terms.