The exit limit is indeed 188 passengers, however the actual maximum capacity for one-class configuration is only 168 passengers. I never seen a 737-400 configured to carry more than 168 passengers before, even on the LCC's. To make this even more make sense, the 737-400 is actually shorter than 737-800 so definitely have the lower seat capacity. (734 length is 36.4m, while 738 is 39.5m - a 3.1m difference)
For details can be seen here, on Page 7 (Inclusive Tour configuration) : https://www.boeing.c...c-passenger.pdf