Can't find a few crypto transactions - some exchanges are gone

[bdp31770]

I'm catching up on taxes from a few years ago. I was on a few crypto exchanges that are now defunct. I never made or lost much money with them, probably just profited or lost $200-$300 in one year.

So, I was just going to leave those off my taxes since I don't know the details. How concerned should I be that that may come back to haunt me? 

Thank you for any feedback.

[LenaH]

Underreporting your cryptocurrency transactions may lead to fines, audits, or other penalties. Unfortunately, not being able to access your trading data from platforms that have been shut down permanently will make accurate reporting more difficult. Your best course of action is to recreate and include all of your transactions on your tax returns to the best of your ability.