I am trying to projected data from Irish National Grid TM65 to WGS 84 Auxiliary Sphere for upload to an ESRI StoryMap. The data was generated as part of a detailed diff-GPS survey and it needs to have an accuracy of 10 - 20cm. However when I use the project tool, and any or none of the geographic transformations, the data is off by about 8 - 12 m to the south east.
I have tried a number of solutions beyond the project tool - opening data into fresh mxd, setting data frame projection, exporting data. I'm wondering if this issue may be similar to those encountered with BNG Why are my OGC® Web Services displaced by about 120 metres? — Esri UK
Any help would be really appreciated.