Their have been a number of topics recently about what is safe to use on celluloid.
I have no idea, as I have never owned a celluloid pen.
However, according to Wikipedia, it is not only pens that have been made out of celluloid, but (until a year a two ago) it was used for table tennis balls.
So, rather than testing your 'solvents' on your beloved celluloid pen, why not test them on table tennis balls instead. (OK, you may laugh now and call me daft, but please tell me why). If this is nothing new to you, the phrase "stop teaching Granny to suck eggs" might be appropriate and I'll go crawl under a rock.
The 'approved' (tournament) balls to look for are those that have the imprint "44", but not "44+" as these are made of a newer plastic. I have no idea about any others.