I've done a lot of work on income tax and people not getting benefits. If you get the GIS numbers monthly from the federal government, you can see. It used to be that the number of people getting GIS dropped every July by 10% and recovered by September. That was people being kicked off because they had not filed their income tax. It gets covered. The data gets filled in, but can you imagine all of a sudden your GIS doesn't show up and you're living on that kind of income?
The other part is, to state the obvious, when you file a tax return and you are a low-income senior, you are not telling CRA anything they don't already know about you: this is what you got from OAS, and this is what you got from CPP. There might be a T5 from a bank, and that's it. CRA could send a completed form to a senior and say, “This is what we have on you from all the T4s. If it's accurate, sign it, and you're done”. This is kind of what they do with GIS now, thank goodness.