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according to BAG, yes. data is accurate
the problem is that in this case it seems to be clearly mismatching actual situation (though not entirely sure how it should be fixed as aerial is not obvious - but it definitely mismatches BAG claims)
you're talking about a tiny shed in a private backyard. if the building appears larger on sattellite, it is possible it was either illegally expanded or a portion of the building is just a roof. (portions that are roof structures don't show up on BAG).
> portions that are roof structures don't show up on BAG
then that data is missing and awaits mapping (together with verifying construction=yes claim at https://www.openstreetmap.org/way/496909279 )