The wall around the opening is what the street sees
In a brick metro the anxiety lives in the masonry rather than in the unit, and almost nobody is publishing anything about it.
Pulling an old wood window out of a brick opening exposes the brick mold, the sill and whatever the lintel above it has been quietly doing for decades. Owners have watched a neighbor's job leave a chipped face at the jamb or a patch of mortar that never matched the wall, and they think about that long after they have stopped thinking about glass.
Say what happens at the edge. What comes off, what is underneath, how the new unit is set and sealed against a hundred year old wall, and what the exterior looks like from the sidewalk once the crew has gone. That is the part with permanent consequences and the part nobody in this trade shows.
Be equally clear about where your work stops. A failing lintel or mortar gone soft at the head is masonry work with a masonry price, and the homeowner's real question is whose name is on that portion of the job. A company that names the boundary in advance is easier to trust than one that discovers it on a Tuesday.
Freeze and thaw is why any of this matters. Water gets into a joint, freezes, and opens it slightly wider each winter, so the sealing detail at the edge of a brick opening either holds for decades or fails quietly. Showing it done properly is content nobody else in this market is making.