HELP Background Check Unique Issue

I worked for a SPAC vehicle. Helped with the initial fundraising/legal/setup etc. process. Got amazing work experience. I had gotten wind of the opportunity through my connections - several rich guys pooling capital for this SPAC. Now here’s the problem since it was being set up etc. I was promised warrants & W2 employment but didn’t really get a contract till later (since we were still setting things up and Covid chaos). Now fast forward in time I’m working a different job and I curiously looked up my background check report. Turns out it only says the dates of me working at the SPAC as the dates I started as a W2 employee (a large discrepancy in months). I had given my bosses number for the background check company, but maybe since the SPAC sponsor entity which was set up for the SPAC no longer exists (given how south the SPAC market went), the background check company did not call my boss but instead used W2 dates from a public domain called Work Number. I attempted to call the background check company and Work Number to try to fix the situation but they said they cannot do anything.

How do I explain this to potential employers and what dates do I put on my resume? Do I need to explain on my resume I transitioned to W2 once the SPAC was set up etc. or is that too nuanced? 

Not sure why this did not raise any red flags at my new employer but want to get ahead of this for future job opps. I only realized this a year later otherwise I would have tried to download/save a bunch of files from my SPAC work laptop as proof but its too late for that.

Feeling really stressed about this and would appreciate the help!