Here's how it shakes out as I understand it:
Player Management: Correct ages, wrong overall
Depth Chart: Correct ages, correct overall
EA Website: Wrong ages, wrong overall
XFN: Correct ages, wrong overall
The Depth Chart is always the definitive source (and naturally the only one other players can't see). But the individual attributes are all the same everywhere except for Pass Block Footwork (as noted below).
It's worth mentioning again: Overall Rating is just a number which is calculated based on a formula derived from the individual ratings. Because a guy is a 95 on Player Management and a 88 on Depth Chart, that doesn't mean he's worse than he appears in PM. He's the exact same player, there's just a bug in how Player Management tallies the overall. The only reason we ask for Depth Chart ratings it to so we're consistently applying an even standard between players and between different trades.
From my investigation, the only individual attribute where the discrepancy occurs is Pass Block Footwork, which is typically inflated on Player Management. I don't know if that accounts for the entire calculation error since I don't know the formula which is used to calculate overall, but it's the only attribute which I've ever seen differing between the two sources. So it would only be applicable for guys where that stat is (O-line, TE).