"Funny, everyone I ask here in Dongbei tells me Putonghua is based on Haerbin speech."

I have found that it's best not to get sidetracked by useless information. Take some linguists (no names no pack-drill) they can go through whole lifespans cluttering up their brains; a bit like a joiner who has bought so many tools ,waxes, fillers that he can't find his knot filler for the life of him: in the same way (or sameish way) our linguist can't actually scrape together enough everyday Mandarin to ask for a custard tart without too much custard in it.