My previous employer had a vesting schedule for the matching portion of the retirement plan. The schedule was setup for vesting at 25% per year of employment. I left between 3 and 4 years, meaning I was only 75% vested in their eyes.
As I was about to request a rollover, I went through the SPD and noticed that it had language defining a year of vesting as being compensated for a minimum of 1,000 hours over the year. I calculated my total hours compensated for the final partial year and it came out to just over 1,000. I contacted the HR department who, unsurprisingly, told me I was crazy and stopped responding to my messages.
My next step was to file a complaint with the department of labor at
https://www.askebsa.dol.gov/WebIntake/ . It took a few months, but they finally got around to sending a letter to the administrator of the plan, and in no time at all I was notified that my vesting level was now set at 100%! I requested the rollover and sure enough the full amount was available - an (almost) instant 33% increase.
Perform your due diligence!