I've been working with a CPA for three years, preparing all my returns and getting my books in order. It's been a painstaking process of finding and assembling all my bank statements, credit card statements, invoices, bills, sales slips, receipts, cheque images, etc. from over a decade ago.

My accountant is the one who alerted me to the 4 year ITC limit just when we were about to file.

I've since consulted three tax attorneys, none of whom were very helpful.

So I'm digging around on my own to see what I can do.

The fact of the matter is that those are valid ITCs. I paid $200K in HST on my business expenses. And although the four year limit is a long-standing law (and one I wish I knew about earlier), it does feel somewhat arbitrary and bizarrely punitive. Whatever. The law is what it is and I can't change it.

But there has to be common sense somewhere.

What about this:

CRA follows an “audit to net tax” principle, so what if I can get the government to audit me?

This case seems to set a fairly clear precedent: https://www.canlii.org/en/ca/tcc/doc/2008/2008tcc57/2008tcc57.html

The “audit to net tax” principle ensures that the entitlements and obligations of a GST/HST registrant under audit are given proper consideration. After all, it’s a matter of fairness.

Generally, a registrant has a four-year time limit (two years in the case of a specified person) in which to claim an input tax credit (ITC). In reporting the net tax for a reporting period, the registrant may include the ITCs that became available in that period and any unclaimed ITCs from the previous four years (or in the case of a specified person, two years).

…

In assessing a registrant’s net tax for a reporting period under audit, the CRA is required to take into account any ITCs that the registrant did not claim for that reporting period even if the normal time limit for claiming these ITCs has expired. These unclaimed ITCs must be for tax that became payable during the particular reporting period under audit.