The mystery was fully answered in a passing comment within the memoirs of Esther Menzies (published in 1974). She explained about this section of the street....
"It was a derelict "feu f'an" they called it. The feu hadn't been paid and the heirs were said to be in Ireland. The houses were about where the police station is. A few of us went in one night. We climbed the rickety stairs, handled the rusty branders and other cooking utensils, touched the old sticky treacle tins, gradually grew silent and crept out."
Who knows how long these lay empty or at what stage the roofs were removed, but these abandoned homes were eventually demolished and replaced with the police house and other houses.