Again you don't understand it because you're actually missing the point. Thanks for proving that multiple times.
If i do literally any other scene lets for instance use Peek2 any variation that would trigger Peek2 unlocks it for the gallery. That is not the case for SadieBlow, Infact SadieBlow is the only scene in the game that runs counter to that.
I literally cannot make you get this any clear than that and if you still don't get it, then let the actual Dev talk to it isntead. Because it's quite clearly a bug with the gallery and how limited this scene is compared to others.
		
		
	 
No problem. You're being stubborn. Only you can't unlock (because you're ignoring the correct path given to you) but everyone else can. That does not make this a bug. And sure, let the Dev's chime in and tell you the exact same thing I have. I tried to help you even loading your save file (which is not going to work since that save is 
NOT going to the party stag). The reason that save won't work is because when Heidi asked if you wanted to go to the party you chose "Sure". To go stag you must choose "No thanks". With your save you NEVER got to label 
sadieblow, so the gallery did not unlock. 
The details further: When you selected "Sure" to Heidi the variable 
halloweenparty is flagged True. This is the first issue with your savefile. To even reach label 
sadieblow then 
halloweenparty MUST be False. Hence how you go to the party stag. You can't go with Heidi, you can't go with Zenda, etc.....you 
MUST go stag.
Until you get over that and your stubbornness then make a playthrough as I mapped for you, you will remain frustrated and think I'm "missing the point". I assure you I am not. I don't create some of the best RenPy mods by overlooking paths or being half-assed. But you do you, I'm done giving up my personal time and trying to help you with this. I wish you well and best regards.
This is your save file scene at the very beginning of label 
halloweenpartystart:
	
		
			
		
		
	
	
		
			
		
		
	
This is the correct "stag" scene at the very beginning of label 
halloweenpartystart (which includes label 
sadieblow):