Thank you very much for the question.
It is very difficult to get accurate information on anybody who is undocumented or in a non-standard living or working situation. The other example that comes to mind is the agricultural sector, where there are many people working in non-traditional arrangements or, for example, who are temporary foreign workers and people living in communal residences. It's just that the way standard surveys are done—like the labour force survey—doesn't capture that. It doesn't go to those homes. When it comes to undocumented workers, I would think that one of the biggest challenges there is simply people not wanting to respond to surveys or not being in the locations where surveyors are going.
I haven't seen any particular data on that, certainly not from official sources recently. Years ago, I remember seeing some estimates on those numbers, but I would have to dig that up and see what that is. Generally speaking, official statistics will miss people in that situation.