"effective date of hire" vs "actual start date"

Hello, I was hired in Feb. 2020 right before the pandemic. My employment contract states that my "effective date of hire" was dependent on me getting my security clearance. Normally that would take 2-3 months but with the pandemic it took more than a year and a half. Furthermore, it is writtent that once I receive my security clearance is when my "start date" would occur. I plan on leaving in near future and there is a clause that states if I leave within 12 months of my "start date" then I need to reimburse them for the security clearance. I'm unsure of the specific semantics used here and wanted to ask if they had any legal ground to ask for reimbursement. Since my first day on the job back in Feb 2020, I have been working full-time employed by the company with full benefits. Wouldn't that have been my start date? Any advice or answers would be greatly appriciated. Thanks.