There has been much discussion on other threads and sites about this topic with a majority of folks believing Howatt bows tend to weigh heavier than marked. It seems everyone has personally owned or seen a mismarked Howatt.
Larry Hatfield, who has been with Howatt/Martin for more than 50 years, will still say they were accurately marked with no intentional low marking.
My guess is they "may" have measured the weight from the front of the riser instead of the inside of the grip. Of all the Howatts I have had experience with, "most" are pretty accurate.
BTW, other makers of bows...such as Bear...have been rumored to have been marked lower than actual weight.
Most likely proof of the theory will never be proven.