Nothing contained in Sections 51-29-131 through 51-29-143 shall be construed as preventing the inclusion, in the boundaries of the drainage district to be extended, of any lands embraced in any other existing drainage district. Any such lands shall be and remain liable to the drainage district in which such land is located for assessments for benefits thereafter levied, by the new district as extended, if any benefits are received by them; and in like manner shall receive credit for any work done, or improvements made, which will benefit the land added to the drainage district as extended.