Yes. (Although my evidence and experience could be a coach vs owner variation).
Evidence: Coach mode first season of Rams. Played Bradford at QB. In the following year, he wanted WAY too much money to renew his contract for talent I felt was mediocre; and I lamented not deciding to just have a new low OVR QB to build up and sign to a longer contract.
In that year, I had Austin Davis as his backup who finished the season with a 71 OVR - having played less than a dozen snaps all year. In the re-signing stage, I decided to sign Davis to a long deal for "pennies" and made the decision not to renew Bradford's contract and stick w/ Davis and draft a new QB.
That season my Rams were moved (by AI owner) to Memphis and became the Egyptians - of which I was bitter about.
I started season one as Rams over again, this time as OWNER mode to avoid that issue happening again.
I made the choice this time to cut Bradford before I started the season eliminating his outrageous contract (which was the last big contract to a 1st overall before the new Collective Bargaining Agreement went into effect).
I started Austin Davis for the season and figured I'd see how good I could make him as a franchise QB for now....
I signed Bradford from FA when the season started to a one-year deal and traded him in week 5 (to the Jaguars for a 2nd and 4th) after I was comfortable that Davis could serve as a QB for my needs (Power Run scheme with a lot of two-TE formations (thanks to Cook and Kendricks).
I made the choice to never upgrade Austin throughout the season - figuring I'd live with what I had for now, and I'd sign him FIRST to a long-term deal at the end of the season then upgrade him. The game "fluctuated" him to a 76 OVR based on his moderate level of success. The off-season I signed him to long term deal, and he wanted significantly more than he did the previous season that finished him with a 71 OVR. Still pennies compared to what Bradford wanted and really not a huge drop off in stats from Sam - and Davis was better mobility which I liked. AWR is irrelevant w/ player controlled QBs, so that was a huge part of the ratings.
When the Off-Season was over, Davis reverted back to OVR 71, but I had 120,000+ XP to assign to him, which bumped him to a 78 once I was done spending it, and better in many ways than Bradford was, and Much Much cheaper.
So in the end I wound up with a 78 OVR QB with a 6 year contract commensurate of a 76 OVR QB, so the game's fluctuation did account for what his XP most likely could have stratified him as, and thus his contract was fairly accurately conceived. However, the fluctuations are smaller from what I can tell than the xp really could achieve so in the end you do save some money by not advancing them even if they have a good season and fluctuate some, but not as much as you would if you didn't advance them and they didn't have a good season or play that much and fluctuate that highly (however you'd have less XP to play with at the end of the season also as a trade-off).
Robert