you can't compare stats and contract money between a FA you lose and one you sign, because for comp picks you only get comp picks when you lose more FAs than you sign
Largely, but not entirely, correct.
Only certain UFAs count in the calculations. The short version is:
* The player must not have been waived by his old team.
* The player must sign a contract with his new team before a certain deadline, and must remain on the team for a certain length of time.
* The player must sign a contract worth at least slightly more than the vet minimum.
No team that has signed more qualifying FAs than it lost has ever gotten a comp pick.
When teams lose more than they sign, they try to "cancel out" contracts as best they can (i.e., a player with a $1M contract will cancel out a $2M contract instead of a $6M contract). [The primary determinant of what round a pick is slotted in is the average annual value of the contract.]
If a team loses as many as it signs, it
may get a late comp 7 if the players lost are significantly better than the players signed.