Use "ENDOFBG1" variable for SoD detection ingame

When transitioning from end of BG1 to SoD campaign, the variable Global("ENDOFBG1","GLOBAL",2) will be set via bdsodtrn.bcs.

So far, I thought I could use this variable to detect ingame whether the game is in SoD or still in BG1.
But, this variable is only set during the transition. Meaning, it is not set if a new SoD game is started.

(Leaving the discussion out of here why the value "2" was used here whereas BGT was using "2" for BGII for years - )

What do you do to detect whether your NPC / mod is in SoD or still in BG1?

Do you see any problems arising if my mod sets Global("ENDOFBG1","GLOBAL",2) at the beginning of Korlasz's tomb for a new SoD game (in BG:EE, not EET) or should I use a different variable altogether?