Why spot converted to CMYK using Gracol could result in different values

The reason is because there are 2 versions of GraCOL 2006 icc profiles.
1. CoatedGRACOL 2006: Signed by Adobe, 2009/6/26
2. GRACoL2006_Coated1v2.icc: Signed by X-RITE, 2007/1/28
tFLOW is including the #2, the official GraCOL 2006 version:
The Adobe version is using different internal settings that results in slightly different numbers since the gamut of the 2 profiles are not identical.

In terms of colors rendering, there should not be any noticeable difference.
Here is a video that shows how setting the 2 ICCs as a simulation profile in Acrobat is giving different values for a converted Reflex Blue spot:
Here is some additional information: