I rolled money from my previous employee to current managed by Fidelity. I have submitted the rollover form with rolled over check along with fund distribution for about 6 months ago. I did not notice this discrepancies until recently when my funds was shrunk. I was working with Fidelity to correct this and they correct it after dealing with them for 2 months. However, recently they reverted back all the adjustments made stating that I am responsible to notify Fidelity within 90 days if I find any discrepancies.
So I am confused now as one time they admitted their mistake and corrected it and now they are saying I am responsible. I was wondering how to proceed with Fidelity or it will be better to seek legal help outside.
I would appreciate any inputs regarding this.

Ask them to show you where it states that you had 90 days to correct any discrepancies. If they do, then tell, them OK, but you want the corrections put back to 90 days prior to your notifying them of the mistakes.

Thanks ScottGem for quick response. Fidelity informed me that they can't do that and it has to be within 90 days.
Also, The online statement that I printed out for quarterly statement does not indicate any 90 day rule to report discrepancies. They informed me that only the Annual statement that they sent out has that information. I did not looked at the statement since I am signed up for "stop printed statements" . I assumed that whatever statement they sent me in mail can be easily pulled from "online statement" feature. At this point I am in dilemma to proceed with legal action or not.

So they are saying that to correct any discrepancy, it has to be reported within 90 days otherwise its can only be corrected from the date of reporting? I'm not sure if you have much of a legal leg to stand on here. But there was recently some new laws making it easier to sue 401K plans so consult an attorney.

Fidelity informed me that discrepancies reported within 90 days will be correct. Anything after that will not be. I made a call out to attorney with my information. They will get back to me with on how to proceed. I will keep this message posted as soon as I get update from Attorney.
Thanks for replying to my questions.