The PRECAMPAIGN tag can control whether a PCC file can be selected or not when used as a standalone line, and can be used more selectively to restrict inclusion of other files from a PCC by using as a |PRE suffix to ABILITY etc lines.

However, it does not have any impact on further PCC lines being included in a PCC file.

Simple way to demonstrate is to create and select just this one campaign file:

1. test pcc to show include options
   CAMPAIGN:test ONE
   GAMEMODE:35e
   TYPE:Dave Griffin.Test

PCC:@/35e/wizards_of_the_coast/rsrd/basics/_rsrd_basics.pcc
PCC:@/modern/wizards_of_the_coast/msrd/arcana/creatures/arcanacreatures.pcc|PRECAMPAIGN:1,INCLUDES=This Text makes no difference

As the campaign 'This Text makes no Difference' is not loaded, the arcanacreatures.pcc should not be loaded at all, unfortunately it is, and gives errors due to lack of other pre-requisites.
(the fact that I'm mixing RSRD and MSRD here is nothing to do with the error, it's just a simple demonstration).

(note my original intent was to modify the MSRD sources so I could load the 'MSRD Basics', 'MSRD FX' and 'MSRD Arcana' without having to load all the creatures 'Modern - Creatures' is the source that arcanacreatures.pcc should have as a PRECAMPAIGN).

Note that there appears to be only two instances in the official sources of a PCC line having a PRECAMPAIGN - these may want to be checked for validity.

pathfinder/paizo/player_companion/elemental_masters_handbook/_elemental_masters_handbook.pcc:PCC:support/pathfinder_unchained.pcc|PRECAMPAIGN:1,INCLUDES=Pathfinder Unchained
starfinder/paizo/starfinder_society_rules/sfs.pcc:PCC:../core/_society/.pcc|PRECAMPAIGN:1,INCLUDES=Starfinder Core Rulebook