Wrote a new tune to my pcm but...

So I have an MPVI2 pro and read the stock file on my Grand Prix. I made some changes to it and wrote it to my pcm without issue. After I wrote it, all history from the pcm was gone as though the battery were disconnected and reconnected. Here's where the issue is: I went to change it back to the stock tune and it said "write complete" but the pcm didn't appear to reset as it did the first time I wrote it and still has the history of miles driven, number of warmups, etc. This makes me wonder if the stock tune is back in or if the previously altered tune is still in there. There's no way to tell from the way the engine runs if it was changed. Will doing a new read (to see what tune is in there now) cause me to have to buy new credits for that new binary file? Is the pcm supposed to reset the stored history each time the tune is changed? Thanks!

you can read as many times as you want with out using credits its when you write were it needs the credits..