These results show that there was only a negligible (and, according to the χ 2 test, statistically insignificant) difference between the results in the cases when the tagger was both trained and tested on "old" corpus and both trained and tested on the "corrected" corpus.
in case one of the tags Middle_1, Middle_2 occurs already in the set Possible_inner_Tags, no action is to be taken, but in case the set Possible_inner_Tags contains neither of Middle_1, Middle_2, both the tags Middle_1 and Middle_2 are to be added into the set Possible_inner_Tags.