From Kellys Directories (Year is publication date and may refer to year before)
1908 The Vento Manufacturing Co, brassfounders, 104-105 Colmore Row.
From subsequent years entries 104.105 appears to be offices occupied by a large number of companies, and not a manufacturing facility.
104-105 is not listed for 1903, 1904, suggesting that in 1908 it was a new building. Similarly the Vento Co is not then listed .
1910 The Vento Manufacturing Co, brassfounders is listed at 25A Witton Road in the commercial listing, but this does not agree with the street listing, in the same volume, which does not list the company there or at the Colmore Row address.
I presume you got your information from the two adverts in the newspaper archives. There seems to be a missprint, in that the numbers of /colmore /row do not go as high as 206, and it probably should be 105