The comparison is inevitable: In the past 18 months, the NFL has investigated its two best quarterbacks of this generation for possible violations of league policy.

Peyton Manning was exonerated Monday because the league determined it had no "credible evidence" that he had been provided with or used any substances banned by its drug policy.

Tom Brady was suspended four games, and gave up on the appeal process earlier this month, after the league determined it was "more probable than not" that he had been aware of an alleged scheme to deflate footballs prior to the 2014 AFC Championship Game. The accompanying Wells report relied on communication logs and other circumstantial details but offered no overt proof of Brady's involvement. Brady has denied all wrongdoing.

So what happened here? Did the NFL play favorites? Why did the NFL issue a 243-page report on Brady's accusations and dismiss Manning's in a four-paragraph release? Is Manning's absolution evidence of a league agenda against Brady and his New England Patriots?

As juicy a story as it might be, I don't think we can make such inferences about the NFL's approach to the two cases. I do, however, think it was no accident that the league noted Monday that Manning and his family "were fully cooperative with the investigation and provided both interviews and access to all records sought by the investigators." (Al Jazeera had reported that human growth hormone was sent to Manning in the name of his wife, Ashley.)

Brady, of course, declined to provide his cellphone to investigator Ted Wells and ultimately discarded the phone. (Brady later said he provided records of all texts and emails Wells requested and that, as a union member, he was under no obligation to set a new disciplinary precedent and turn over the device itself.)

The Patriots, meanwhile, declined to make two game-day employees available for follow-up interviews after new developments arose. NFL commissioner Roger Goodell equated that lack of cooperation with supporting "a finding that [Brady] had sought to hide evidence of his own participation in the scheme."

Ultimately, Brady and Manning were investigated under the terms of separate league policies. Brady's violation fell under the league's policy for integrity of the game, which carries a "more probable than not" standard for guilt. Manning was investigated under the policy for substance abuse, which requires either a positive test, a missed test or behavior "which, in the judgment of the [policy] medical director, exhibits physical, behavioral, or psychological signs or symptoms of misuse of substances of abuse," according to the policy.

Admittedly, there is a subjective nature to each possible violation. "More probable than not" can be interpreted in different ways. One medical director's judgment of a player's behavior could be different from another's. And while at first glance a drug issue seems more serious than deflating footballs, both convictions would imply cheating -- something no player wants as part of his legacy.

Unless there is evidence that hasn’t yet been made public, the NFL seems to have had little wiggle room in the Manning investigation. The story originated with an intern from an Indianapolis clinic who almost immediately recanted his story. You'll hear no suggestion from me that the NFL is whitewashing Manning to protect him. There's just no meat here.

There was relatively little meat on the bones of the Brady investigation, either. But if there's a takeaway to be had in this comparison, it's that full cooperation carries substantial weight with the NFL, and with Goodell in particular.

This isn't new. You might recall that in 2010, Goodell fined quarterback Brett Favre $50,000 for failing to cooperate fully with an investigation into whether he harassed a female New York Jets employee. In that announcement, the NFL said: "On the basis of the evidence currently available to him, commissioner Goodell could not conclude that Favre violated league policies relating to workplace conduct."

The league would have you believe it has more than enough evidence on Brady to suspend him, but we've been down that road before. Fair or not, Deflategate might have ended differently if Brady had handed over his cellphone and the Patriots had submitted to every interview requested.

Each had his reasons to refuse. Brady's personal privacy and his status as an active member of the NFL Players Association were particularly compelling. Manning, who is retired, had no such concerns. Notably, the NFLPA released a cryptic statement Monday that suggested active players have rights to a process that a now-retired Manning might not have been concerned about.

In the end, Peyton Manning will go untarnished after an allegation for which no one has found merit. Tom Brady will sit four games, ostensibly because he was generally aware of an alleged scheme to cheat but more likely because he did not submit fully to the league's fluid investigative structure in the aftermath. And so it goes.