It will have grown substantially since time of purchase.

One part I'm unclear on is that I've heard the recapture can be substantially more than the tax benefits received. 

If it’s an innocent omission and an expense that you can easily substantiate I would not be dissuaded from amending the return due to any perceived audit risk if all else is good and you are confident in any tax positions taken, as applicable. 

If you have a STR where you are providing substantial services - Potentially.

I'm currently in the process of going back to school to get certified in a new career, and I've also recently come into a pretty substantial inheritance.

Utility companies even with no leaks are raising the per gallon usage charges upping the bills substantially.

Collected substantial sign-up bonuses.

But that's if you have a substantial assets.

No substantial experience in the field so far, but expecting to put all the theory learnt into practice soon. 

., substantial affiliate kickbacks) and perform at least a modicum of due diligence on the provider (# podcast appearances aren't too helpful; check if their background to see if it's aligned with their claimed expertise, etc.)