A legal, permitted two-family home with documented rental income is priced through an income approach, comparing net operating income against similar multi-unit sales, while an unpermitted suite is valued closer to a single-family home with useful but unverified extra space. The gap between those two outcomes on the same house can be substantial.
Condition and location still matter as much as they do for any home: an older two-family property with deferred maintenance competes against newer suburban builds with legal suites already in place, and buyers weighing both will price in the difference in remaining useful life on the roof, furnace and windows regardless of the rent roll.
The only reliable number for your specific property comes from comparable multi-unit sales and verified income, not a citywide average that was never built to price this kind of home. Get your hand-reviewed valuation from Joel Dyck.