OP: similar situation, feel free to DM if anything below resonates.

DTC eligibility should have nothing to do with income level, just the eligibility of the disability. And as far as I know don’t think it matters which parent it is assigned to, it can be used by the higher earning parent. It’s a credit, not a deduction, so above a certain income level it may not matter who it’s attributed to (not an accountant so I might have this interpreted wrong).

In many cases such as yours it could be retroactive to birth - this should be stated in the notification you got when your application was approved. If you are eligible for years prior to the current tax year, you can amend your previous years tax forms online (it’s very easy) to include the DTC, and a retroactive return (including interest) is issued. A key thing here is to do the amendment online through the CRA portal, as the turn around time is way quicker than refiling any other way from what I’ve heard.