Missing roof stack
I live in a victorian that was remodeled in the inside before we purchased the home three years ago. We've recently noticed a foul smell coming from the first floor bathroom. When we called our plumber, he thought is was probably due to a clogged roof stack. We had a roofer come check (the roof is too steep for a layman to access), but he informed us that he could not find a roof stack anywhere. Next, we had our plumber come and based on his assessment he thought the smell was due to a dead animal rather than anything to do with the drain-waste-vent system. He said the smell was definitely not sewage.
My question is, how is it possible not to have a roof stack? I've been in this home for three years and one would think that the house would smell like sewage/methane constantly if this were the case. Does anyone have experience with this problem? Where could the system be terminating if not through the roof?