JCp-1-NP is a commercially distributed pressed nano-powder pellet calcium carbonate reference material. It is widely used as a matrix-matched reference material in Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) analyses, yet its composition is not well-documented. In this study, we report the uncertainty of the pellet composition by analysing 20 element-to-Ca ratios measured in three different laboratories. The interlaboratory comparison dataset was outlier-corrected and provides a robust assessment of the composition and long-term stability of this nano-powder pressed pellet. In addition, a review of all publicly available compositional data using this reference material published so far is compiled. The dataset is available online at the Figshare repository.