Most subdistricts created in one province in a year?

Still working through the many subdistrict creation announcements, another notable peculiarity showed up. In 1975 a total of 15 subdistricts were created in Lopburi province, and another 8 the following year, while normally especially in such a rather small province only one or two subdistricts got created in one year. Even more striking is the fact that these subdistricts 15 were created in the single district Chai Badan, which at that time covered the whole northeastern part of the province - Lam Sonthi and Tha Luang were split off in 1978 and 1989 respectively. In fact all of the subdistricts which were split off when creating Tha Luang were created in these two years. In 1974 Chai Badan just had 8 subdistricts, in 1976 the number has increased to nearly the threefold. And another 3 subdistricts just date back to 1970, another one to 1971. So taking these in account as well, the number of subdistrict multiplied to the sixfold within 6 years.

However I have no idea what was the reason behind this big increase of subdistrict numbers in those years, it cannot be the improved irrigation possibilities after the construction of the Pasak Jolasit Reservoir, as that was initiated in 1989.