So, when converting NMT fumarate to freebase I have been mixing the fumarates with sodium carbonate, adding water to make a paste, letting the past dry, then pulling 3x with acetone, filtering acetone, then evaporating.

My question was whether or not the fumaric acid will be soluble in the acetone or if it will instead stay behind as sodium fumarate.

I made some enhanced leaf with 3.01g of NMT fumarate (2.26g NMT) and 1.51g of mullein, with the goal of a 1.5:1 NMT/leaf ratio. After converting the fumarates and evaporating onto the leaf, I had a resulting total mass of 3.84g, which means that 2.33g of material was deposited on the leaf. So, I'm wondering if some of the extra mass could be fumaric acid. I suppose I could always wash the leaf with water to clean it.

It could be 70mg of water?? How dry was your leaf to start with? Has the weather become more humid since then?

Was your acetone anhydrous, freshly distilled? How dry was your mix with sodium carbonate when pulled? Did you filter your acetone pull? Sodium fumarate might have come along with it somehow - either in suspension or solution, or both. I doubt it's free fumaric acid in your leaf.

Has the NMT absorbed oxygen from the air, maybe?

Moisture plus sodium fumarate plus a bit of oxidation and, possibly, non-volatile impurities from the acetone could possibly add up to 0.07g. Also bear in mind the accuracy of your scales...

It was more of a question of whether there is anything that is soluble in the acetone (assuming it is anhydrous). I'm not worried about the extra mass though.

Lots of things are soluble in acetone... And you can't always assume it's anhydrous. But, given the circumstances, I'd be very surprised if you had any free fumaric acid knocking around. How would it have been formed?