Just thought of an explanation Mike and added it to my earlier post. The Lozells Chapel the retiring reverend referred to could be the Aston Villa (George Street) Chapel, Lozells. The map you've just posted makes it clear there was no early mission chapel on the Lozells Street site, thanks. It dispels my 'wonderings' about whether there was an early chapel. I thought it might have been a chapel that had outgrown itself (hence the use of the school across the road). This was all sparked by the reverand's comment which made me question the early history of the site !
So that would seem to confirm the first dedicated Mission building in Lozells Street would be that of 1894. It also helps to confirm that the listed building details must refer to the 1894 part of the site, not the later 1909 extension. The date of the extension to the west of the 1894 building is unknown - although seems be shown on the 1902 map. It has the appearance of an extension as its a peculiar shape to have been included in the original 1894 design.
Another point going back to the earlier Porchester Street 'cottage'. A cottage seemed to be a feature of the earlier organisation of services and preaching. The meeting room(s) at the Porchester Street house would have been in the group of meetings known as cottage services, other forms were meetings in the open air while others were visits to people in their homes. This sort of organisation would make sense if there was no dedicated Chapel nearby for members to congregate until the Mission started to make use of the Lozells Street Board School (built in 1882). Viv