That is the grip end changing what the scale reads.
Each wrap of full grip tape or full build up tape is 1.5 grams = 3 grams of 1.5 SW points.
Maybe the split grip isn't fully seated
There is also the grip solvent to factor in while it sets.
A properly epoxied club really only adds .75-1 gram...it really isn't a fact unless you put WAY too much in.
I SW everything with 2 wraps of tape & a 52ish gram weight. If i hit my desired SW there I just build the club.