PaulsenAfter some internal discussions with members of the ozfortress community (including the head admin) we think there is a stat missing from logs.tf that can actually provide a lot of useful information: buffs.
Taken form this game http://logs.tf/1998335 this is what a tf2 log healing event looks like
L 04/04/2018 - 19:44:12: "SoLe<464><[U:1:3624870]><Blue>" triggered "healed" against "Paulsen<469><[U:1:35306962]><Blue>" (healing "24")
I'm not sure how you determine from that whether the heal event is a buff or healing from a damaged state. The logs don't give player health totals, and they also don't record all damage events (self damage, world damage, etc) so you can't reliably calculate it from context.
One possibility might be that overhealing always heals for certain amounts, but that would require some research to establish whether they were different from a normal healing event. Even if that were the case healing rates between normal max health and overhealed health probably also vary by medigun (which isn't shown by logs unless there is an uber) and the class being healed, so it's hard to reliably extrapolate a healing event as as being a buff by it's amount without adding a lot of game knowledge to the parser and making it more brittle and error prone.
I don't think it's possible without a modification to server plugins to mark healing events as being overheals or not, and they don't receive much support these days.