Searching for Cheryl is an unmarked quest in Fallout 3 and it appears that the second log of the quest could not be found on the console it was supposed to be. The third grave that contains Search party log #4 is not found as well.
Because of it, it is unknown if the corpse of Manny Koch would be spawned or not
Quest info:
http://fallout.wikia.com/wiki/Searching_for_Cheryl
Load Order as follow:
[X] FalloutNV.esm
[X] DeadMoney.esm
[X] HonestHearts.esm
[X] OldWorldBlues.esm
[X] LonesomeRoad.esm
[X] GunRunnersArsenal.esm
[X] Fallout3.esm
[X] Anchorage.esm
[X] ThePitt.esm
[X] BrokenSteel.esm
[X] PointLookout.esm
[X] Zeta.esm
[X] TaleOfTwoWastelands.esm
[X] DragsVGUArmorBase.esm
[X] Project Nevada - Core.esm
[X] Project Nevada - Cyberware.esp
[X] Project Nevada - Rebalance.esp
[X] Project Nevada - Extra Options.esm
[X] iHUD.esm
[X] AWorldOfPainFO3.esm
[X] TTW_XPReduction.esp
[X] TTW_SuperMutantRebalance.esp
[X] TTW_StartupMenu.esp
[X] TTW_SpeechChecks.esp
[X] TTW_OutcastTrading.esp
[X] TTW_MoreCookingItems.esp
[X] Project Nevada - Cyberware Additions.esp
[X] Project Nevada - Rebalance Complete.esp
[X] Project Nevada - All DLC.esp
[X] Project Nevada - TTW.esp
[X] CASM.esp