It has changed. Under the vacation policy, we couldn't be forced to take vacation time when we were off hurt or sick. The change to the PTO system gave management the ability to "dock" us PTO time for being hurt, sick, or even off for FMLA without our approval. They can even take partials to make an 8 hour day if you left work early.
I was told any banked time before 2017 goes to a legacy bank that cannot be touched until your present PTO is zero. Like you take a week off and only have 20 hour presently, the additional 20 would come from your legacy bank. The legacy bank cannot be lost due to separation from the company and would be paid out.
Any time that you roll over and bank after 2017 will be absorbed (taken) by the company for separation of ANY reason, whether you quit, retire, or are terminated. Basically, use it or lose it policy. You can still bank or roll over time, it's just a gamble.