We suggest an explanation based on the Blume-Capel model of why some layered compounds of the iron-intercalated transition metal dichalcogenides TaS2(Se2) exhibit spin-glass behavior, while another group of this family demonstrates low-temperature paramagnetism. In these materials, the doped Fe atoms either substitute the Ta atoms with losing their magnetic moments or sit between the TaS2(Se2) layers keeping their spin states. The Blume-Capel model allows us to introduce a chemical potential to control a balance of the intercalated elements of both types. The Ghatak-Sherrington theory of spin-glass behavior of this model predicts an existence of a tricritical point that means that there is a concentration threshold of Fe ions retaining their magnetic moments, above which spin-glass ordering occurs. Below the threshold, Fe ions behave as independent paramagnetic centers. We build temperature dependencies of magnetic susceptibility and field dependencies of magnetization to highlight specific features of the model related with a variable content of Fe ions in the high-spin state. A specific crystal structure of the layered transition metal dichalcogenides gives an opportunity to increase the concentration of ions with nonzero magnetic moments by co-intercalating non-Kramers 3d ions into the van der Waals gaps. This process may trigger spin-glass ordering in the initially paramagnetic Fe-doped TaS2(Se2) polytype complexes. © 2024 American Physical Society.